systemic-game-design-course/docs/research/hearthstone.md

Hearthstone rules research (for the systemic-design course)

Researched 2026-10-28. Pages were fetched with WebFetch. WebFetch only returns quotes of 125 characters or fewer, so all "verbatim" quotes below are short excerpts. Longer passages are paraphrased and marked as such. Before publishing, re-check any quote that matters against the live page.

Fetch log

Source	Result
https://hearthstone.wiki.gg/wiki/Advanced_rulebook	Loaded. About 480k characters, read in full in 100k chunks. Last edited 26 June 2026.
https://hearthstone.fandom.com/wiki/Advanced_rulebook	FAILED (HTTP 402).
curl of wiki.gg ?action=raw	FAILED. wiki.gg served a "Blocked" page.
https://www.reddit.com/r/hearthstone/comments/3be8cr/... (Patashu)	FAILED. The tool cannot fetch from reddit.com.
old.reddit.com version of the same	FAILED. The tool cannot fetch from old.reddit.com.
web.archive.org copy of the Patashu thread	FAILED. The tool cannot fetch from web.archive.org.
https://www.reddit.com/r/hearthstone/comments/1wf8f4k/ and /1wh6bq2/ (Assemble threads)	NOT FETCHED. reddit.com is blocked for the tool. A web search did not surface them either.
https://hearthstone.wiki.gg/wiki/Baron_Rivendare	Loaded. Last edited 26 Sept 2023.
https://hearthstone.wiki.gg/wiki/Assemble	Loaded. Last edited 22 Oct 2026.
https://hearthstone.wiki.gg/wiki/Mismatcher, /Fleshshape, /Rajh	Loaded.
https://news.blizzard.com/en-us/article/24304163/ ("Reign of the Black Empire Is Now Live!")	Loaded. Only marketing copy, with no mechanical detail.
https://us.forums.blizzard.com/en/hearthstone/t/166766 (37.0 patch notes thread)	Loaded. Only player complaints, with no rules.
https://www.playnews.gg/en/guides/hearthstone-assembly-how-does-the-reign-of-the-black-empire-keyword-work	FAILED (HTTP 403).

The Patashu "When do minions die?" post could not be read, so nothing in this file is sourced from it. The Advanced rulebook is the community document that grew out of that kind of testing, and it is the source used below.

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Source 1: Advanced rulebook (hearthstone.wiki.gg)

URL: https://hearthstone.wiki.gg/wiki/Advanced_rulebook

Summary.

• A player action starts a Sequence. A Sequence is made of Phases.
• Each Phase or Event builds a Queue of every trigger that can respond, ordered by order of play. Order of play means when each trigger's entity entered play, oldest first.
• Once the first entry in a Queue starts resolving, the Queue is locked.
• Resolution is depth-first. A trigger's consequences are fully explored before the next sibling in the Queue resolves.
• Phases can nest. Deaths are only processed when the outermost Phase ends. At that point the game runs three steps in order:
  1. Aura Update (Health/Attack)
  2. Death Creation Step
  3. Aura Update (Other)
• If anything died, a Death Phase resolves the Death Events in order of play. A Death Phase is itself an outermost Phase, so this repeats until no new deaths occur.

Quotes (verbatim, short):

• Sequence: "A Sequence is what begins when a Player Action is taken."
• Phase: "Phases are surrounding blocks created whenever one or more triggers/Events are raised."
• Queue: "A Queue is a sequential container where multiple simultaneous triggers or Events are held."
• Rule 2a: "A Queue is created and filled with all triggers that can respond, in order of play."
• Rule 2c: "A Queue becomes immutable once Hearthstone starts to resolve the first entry in it."
• Order of play: "Order of play means the order the Entities each Event/trigger is associated with entered play, from oldest to newest."
• Exceptions to order of play:
  • Redemption "always Queues last". The rulebook's wording is that "all triggers follow order of play exactly" apart from Redemption.
  • Poisonous "resolves in a queue with higher priority."
• Depth-first: "The process of resolving an event is similar to a depth-first search"
  • Also: "the need to resolve an event before starting the next is a depth-first resolution."
  • A newly raised event "immediately begins exploring its consequences, before resolving those remaining for the current trigger/Event."
  • The rulebook contrasts this with: "(If multiple events could be partially resolved, that would be breadth-first)"
  • Also: "a trigger cannot be nested inside itself"
• Outermost Phase:
  • "When the outermost Phase resolves, Hearthstone will run several Steps, including processing Deaths and updating Auras."
  • "but only the outermost Phase ending initiates the Death Creation Step."
  • "After the outermost Phase ends, Hearthstone does an Aura Update (Health/Attack), then does the Death Creation Step." Aura Update (Other) follows the Death Creation Step (Rule 4a).
• Death Creation Step:
  • It "Looks for all mortally wounded (0 or less Health)/pending destroy (hit with a destroy effect) Entities"
  • It then "sends them from play to the graveyard and creates Death Events for each."
• Mortally wounded:
  • "mortally wounded and pending destroy are ONLY converted into dead once the outermost Phase ends!"
  • "negative (damaging/destroying/hindering/misdirecting) triggers ignore mortally wounded and pending destroy characters."
  • "However, 'beneficial' (healing/buffing) triggers count mortally wounded, and AoE effects count mortally wounded."
• Death Phase chaining:
  • Glossary, Phase: "Then if any Deaths occurred, a Death Phase starts, resolving Death Events in order of play."
  • Glossary, Phase: "This continues until there are no new Deaths."
  • Glossary, Death: "Because a Death is an Event, a new Phase begins where all simultaneous Deaths are Queued."
  • All "Death Event triggers (Deathrattles, on-Death Secrets and on-Death triggered effects) are Queued".
  • Combat section: "death processing is not done in the middle of a Phase, but is done between Phases".
  • Forced Death Phase: "no follow-up Death Phases can be scheduled until the outer Phase ends".
  • Example: "At the end of the Death Phase, Hearthstone checks for additional deaths"
• Auras:
  • "whenever a minion is summoned (but not played), Hearthstone updates both kinds of Auras."
  • "Auras are not recalculated due to minions leaving play or due to minions being stolen in the middle of a Phase."
  • "Enchantments apply and modify Health/Attack/Mana costs the moment they are attached."
  • Baron Rivendare is listed among the Aura Update (Other) auras (Rule 4c).
• Trigger-doubling cards (Rule 4d notes):
  • "Cards that trigger effects multiple times, like Brann Bronzebeard, Baron Rivendare and Drakkari Enchanter, check before an Event starts."
  • "This means if one Battlecry/Deathrattle/End of turn effect summons them, it will not trigger again."
  • "But Deathrattles/End of turn effects that follow can benefit, for Aura (Other) is updated when you summon them."
• AoE damage (Rule DH1, paraphrased with an embedded quote):
  • For AoE, "all of the Damage/Healing Events are created in play order", and they are then resolved in play order.
  • Rule DH3 exceptions: Lightning Storm, Elemental Destruction, Dark Iron Skulker, and Lightbomb resolve each Damage Event as soon as it is created, in play order. They still pick their targets first.
• Flamestrike / Armorsmith example: "the Armorsmiths will be mortally wounded but remain in play, triggering on each Damage Event"
• Frothing Berserker example (Arcane Explosion): "all the damage occurs, then each 'On Damage' Event is resolved based on the order of play."
• Acolyte of Pain example (three Unstable Ghouls dying in one Phase): the Acolyte "is hit, triggered and draws three cards" before it dies.
• Predamage (DH7): "Just before a Damage Event is created, Predamage triggers will queue and resolve in play order."
• Combat damage:
  • On damage taken: "the defender ALWAYS triggers first, regardless of order of play."
  • On damage dealt: "the attacker ALWAYS triggers first, regardless of order of play."
• Summon position:
  • Deathrattle summons appear "in the board position the Death Event remembered from when it was created."
  • "Feign Death and similar effects summon minions at the right side of the board, not the minion's position."
• Summon Resolution Step: it "occurs after the first Aura Update (Health/Attack) but before Death Creation Step".

Topics not found anywhere in the rulebook: the terms "Pre-phase" and "Main phase", Whirlwind specifically, and a Baron-dies-simultaneously example. The Baron case is covered on his card page (Source 4).

Source 2: Patashu, "Hearthstone Science: When do minions die?" (reddit)

URL: https://www.reddit.com/r/hearthstone/comments/3be8cr/hearthstone_science_when_do_minions_die_20_minute/

NOT LOADED. reddit.com, old.reddit.com and web.archive.org are all blocked for the fetch tool. Nothing in this file comes from this source. Do not cite it in the course until someone reads it manually.

Source 3: Assemble (Reign of the Black Empire)

3a. Reddit threads 1wf8f4k and 1wh6bq2

NOT LOADED (reddit.com is blocked). A web search did not surface them.

3b. Wiki: https://hearthstone.wiki.gg/wiki/Assemble

Loaded. Last edited 22 Oct 2026. Added in Patch 37.0.0.254477 (2026-10-13).

Reminder text (verbatim): "Get a random minion. Change half its text."

How it works:

• It "adds a random minion to the hand, then presents two other minions."
• The added minion "can have either the top or bottom half of its text replaced with the corresponding text from either presented minion".
• Paraphrased: the minion keeps its own stats, cost, name, art, rarity, and minion type. Only the text changes.

Constraints (paraphrased unless quoted):

• The pool is about 250 curated minions whose effects can be split in half.
• "The Assembled minion must have to have its text altered." The typo is in the source.
• The presented options cost the same as the main minion or up to 2 more. For 9- and 10-cost minions, the options can cost 8, 9, or 10.
• As with Discover, the minions are from your class or neutral unless the card says otherwise.
• When a card names a pool (for example, Fleshshape's "Deathrattle minion"), only the middle (default) minion must come from that pool.

Not specified on the page: what exactly "top half" and "bottom half" mean. The page does not say whether the split is trigger vs effect or first line vs second line, and it gives no worked text example.

Cards with Assemble (13): Chisel, Darkest Depths, Sandcrafter, Shadowcrafter, Steward of the Vale, Thaw From Ice, Tinker, Attentive Tender, F3TCH3R, Fleshshape, Shadow Sculpt, Mismatcher, Rajh.

3c. Example card pages (wiki.gg)

• Mismatcher (Priest, Epic, 5 mana 4/6 Aberration): "Taunt. Battlecry: Assemble a minion that costs (3) or less with cards that cost (5) or more."
• Fleshshape (Death Knight, Rare spell, 3 mana): "Assemble a Deathrattle minion. Give all minions in your hand +2/+2."
• Rajh (Paladin, Legendary, 5 mana 4/4 Titan-forged): "Battlecry: Assemble a minion from any class. Transform it into a Passive Hero Power."
  • Note: "Rajh Assembles a minion from a smaller pool that includes no Battlecry or Deathrattle effects."

3d. Blizzard news: https://news.blizzard.com/en-us/article/24304163/

Loaded ("Reign of the Black Empire Is Now Live!"). It has no mechanics.

• "Create minions unlike any Hearthstone has seen before with the new Assemble keyword."
• "Combine minions from a curated pool to build custom creations."

Source 4: Baron Rivendare (wiki.gg)

URL: https://hearthstone.wiki.gg/wiki/Baron_Rivendare. Last edited 26 Sept 2023, so newer changes may be missing.

Card:

• FP1_031, Curse of Naxxramas. A Core version, CORE_FP1_031, also exists.
• 4 mana 1/7 Legendary, Undead (minion type added in Patch 25.0, 2022-11-29).
• Text: "Your minions trigger their Deathrattles twice."

Notes:

• Simultaneous death: "However, if he dies at the same time as a minion with a Deathrattle, the Deathrattle is not doubled."
• "Baron Rivendare's effect, being an aura, only appears and disappears between Phases when Aura Update (Other) runs". The page says this runs just after the death-processing step.
• Queuing, paraphrased: "The two activations of the Deathrattle do not queue/resolve separately". The Deathrattle queues once, and when it resolves, the aura makes it activate twice.
• "The second activation of the Deathrattle is immediately after the first activation resolves", which is before the next queued Death trigger.
• "Both Deathrattles are treated separately." For example, Webspinner can produce two different cards.
• "Rivendare's ability is not duplicated or multiplied by having more than one Baron Rivendare in play."
• "Baron Rivendare's effect also works on remotely triggered Deathrattles such as from Play Dead."

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Answers

a. Does a Deathrattle trigger twice if Baron dies in the same AoE? No.

• The Baron page says: "if he dies at the same time as a minion with a Deathrattle, the Deathrattle is not doubled."
• Mechanism, from the rulebook:
  • Baron's doubling is an Aura (Other).
  • At the end of the outermost Phase, the order is Aura Update (Health/Attack), then the Death Creation Step (which removes Baron together with the other minion), then Aura Update (Other).
  • Aura Update (Other) runs after Baron has left play, so his aura is gone before the Death Phase resolves the Deathrattles.
  • The rulebook also says doubling cards "check before an Event starts."

b. In what order do triggers resolve, and is it depth-first?

• When an Event (or a set of simultaneous Events) occurs, a Phase is opened. A Queue is filled "with all triggers that can respond, in order of play" (oldest entity first). Simultaneous Events are queued in order of play, and so are each Event's triggers (Rule 2b).
• Exceptions: Redemption always queues last, Poisonous has higher priority, and in combat the defender's on-damage trigger goes first.
• The Queue locks once resolution starts. Minions summoned mid-resolution cannot join it.
• Resolution is depth-first: each trigger's resulting Events open nested Phases that resolve completely before the next sibling trigger.
• Deaths are not processed in nested Phases. They wait until the outermost Phase ends.
• The rulebook does not use the terms "Pre-phase" or "Main phase". It does have Predamage triggers, which queue and resolve in play order just before a Damage Event is created.

c. When are mortally wounded minions removed, and how do Death Phases chain?

• A minion at 0 or less Health is "mortally wounded" and stays in play. AoEs and beneficial triggers still count it, while negative triggers ignore it.
• When the outermost Phase ends, the game runs Aura Update (Health/Attack), then the Death Creation Step, then Aura Update (Other).
• The Death Creation Step removes every mortally wounded or pending-destroy entity at once and creates a Death Event for each.
• A Death Phase then queues all on-death triggers (Deathrattles, on-Death Secrets, on-Death triggered effects) in order of play.
• The Death Phase is itself an outermost Phase. If its Deathrattles mortally wound more minions, another Death Creation Step and Death Phase follow, "until there are no new Deaths."

d. How does "trigger twice" work (Baron, Brann, Drakkari)?

• These are auras in the Aura Update (Other) category. They "check before an Event starts."
• If one of these cards is summoned by a Battlecry, Deathrattle, or End of turn effect, that same effect does not trigger twice. Later effects in the same Sequence can benefit, because summoning updates Aura (Other).
• For Baron, the Deathrattle is queued once. When it resolves, the aura makes it activate twice in a row (two separate activations, back to back) before the next queued trigger.
• A Baron who is summoned or stolen mid-Phase only starts or stops doubling at the next Aura Update (Other).
• Rules caveat: the Baron page describes the doubling as applied at resolution of a single queue entry, while the rulebook says "check before an Event starts". Both rule out a doubling source that appears mid-Event. The precise "queue time vs resolve time" distinction is not stated more explicitly in either source.

e. How does Assemble work?

• Reminder text: "Get a random minion. Change half its text."
• A random minion (class or neutral, from a curated pool of about 250 minions with splittable text) is added to your hand. You are then shown two other minions.
• You replace either the top half or the bottom half of the added minion's text with the corresponding half from one of the two presented minions.
• The base minion keeps its own cost, stats, name, art, rarity, and type. Its text must change.
• The presented options cost the same as the base minion or up to 2 more.
• Pool restrictions on the card apply only to the base minion.
• Examples:
  • Mismatcher: "Taunt. Battlecry: Assemble a minion that costs (3) or less with cards that cost (5) or more."
  • Fleshshape: "Assemble a Deathrattle minion. Give all minions in your hand +2/+2."
  • Rajh: "Battlecry: Assemble a minion from any class. Transform it into a Passive Hero Power."
• None of the sources I read defines whether a "half" means trigger vs effect.

f. Other teaching-useful details

• AoE damage: all Damage Events are created first, in play order, and then resolved in play order. So a Flamestrike with two Armorsmiths on board grants armor for every Damage Event before the Armorsmiths die. Frothing Berserker with Arcane Explosion follows the same "all damage, then each on-damage Event in order of play" pattern.
• Acolyte of Pain draws once per Damage Event, even when it is mortally wounded by an earlier one.
• Lightning Storm, Elemental Destruction, Dark Iron Skulker, and Lightbomb are exceptions: they resolve each Damage Event as soon as it is created.
• In combat, the defender's on-damage trigger goes before the attacker's, regardless of order of play.
• Deathrattle summons appear at the dead minion's remembered board position. Feign Death-style effects summon on the right side of the board.

Draft claims that are WRONG or unverified

1. "If Baron Rivendare and Loot Hoarder die to the same 1-damage AoE, Loot Hoarder's Deathrattle triggers only once because Baron is removed in the Death Creation Step before deathrattles queue."

   • The outcome is CORRECT: the Baron page says "the Deathrattle is not doubled".
   • The stated reason is IMPRECISE. The cause is that Baron's doubling is an aura, and Aura Update (Other) runs after the Death Creation Step removes him. His aura is therefore gone when the Death Phase resolves.
   • Suggested rewording: "...because both are removed together in the Death Creation Step, and the following Aura Update (Other) removes Baron's doubling aura before the Death Phase resolves Deathrattles."
   • Also note: Loot Hoarder is 2/1 and Baron Rivendare is 1/7, not 1 HP. The draft's "1 HP each" is wrong for Baron, so a 1-damage AoE would not kill him. Fix the example, for example by using a 7+ damage AoE, or by saying "both die in the same AoE".

2. "Triggers are ordered by play order and resolved depth-first."

   • MOSTLY CORRECT.
   • The rulebook term is "order of play" (when each entity entered play, oldest first).
   • Add the caveats: Redemption queues last, Poisonous has priority, and the combat defender triggers first.
   • Queues lock once resolution starts.
   • Deaths are deferred to the end of the outermost Phase, so depth-first does not mean deaths happen mid-chain.

3. "Mortally wounded minions stay on board until the outermost phase ends, then Death Creation Step removes all simultaneously in play order and queues Deathrattles."

   • Largely CORRECT, with these corrections:
     • (i) An Aura Update (Health/Attack) runs before the Death Creation Step. A minion can be saved or killed by an aura change at that point.
     • (ii) Pending-destroy minions are included, not just mortally wounded ones.
     • (iii) The Death Creation Step removes them and creates Death Events. A Death Phase then queues and resolves the on-death triggers in order of play. That includes Deathrattles, on-Death Secrets, and on-Death triggers, not only Deathrattles.
     • (iv) The process repeats until there are no new deaths.
   • "Removes all simultaneously in play order" mixes two things. Removal is simultaneous. The order of play applies to how the Death Events and their triggers are queued.

4. "Assemble splices the top half (trigger) of one card with the bottom half (effect) of another."

   • UNVERIFIED / likely MISLEADING.
   • The wiki says the base minion (randomly generated) keeps its stats, cost, name, and type. Either its top or its bottom half is replaced with the corresponding half of one of two presented minions.
   • So it is not "top from card A plus bottom from card B" in a fixed direction. The player chooses which half to replace, and it is a base card plus one replacement half.
   • No source I read defines a half as "trigger" vs "effect". Do not make that claim until it is verified, for example from the reddit threads (which could not be loaded) or from in-game testing.

The Patashu reddit post and both Assemble reddit threads remain unread. Any course claim attributed to them needs a manual check.