Possession

Contract

Apos is TFT/ROC CAbilityPossession (parent AAsm). ACps is an AbilityData alias whose code is Apos, so it shares CAbilityPossession and reads its own row through abilityitem_t.code.

Aps2 is TFT-only CAbilityPossessionTwo (parent Apos, own code=Aps2). It is not an Apos alias and is not Charm (ANch / CAbilityCharm).

Rawcode	Archive	Class	Channel	Effect
Apos	ROC and TFT	CAbilityPossession	no	immediate ownership transfer; caster dies
ACps	ROC and TFT	CAbilityPossession (code=Apos)	no	same; creep cost/tooltip row
Aps2	TFT only	CAbilityPossessionTwo	yes (AB_CHANNEL)	stun lock for Dur, then transfer; caster dies

Shared targs: ground,nonhero,enemy,organic,neutral. Air, heroes, mechanical, allies, dead, and spell-immune units are invalid. DataA is max allowed UnitBalance.level (stock 5); level 0 disables the gate.

Aps2 channel fields (OE)

Field	Stock	OE label	Runtime
DataA	5	creepMaxLv	same max-level gate as Apos
DataB	1.66	damageIncrease	caster attack-damage taken multiplier while Bpoc is active
DataC	1	invulnerable	non-zero → target invulnerable for the channel
DataD	1	magicImmunity	non-zero → target spell-immune for the channel
BuffID	Bpos,Bpoc	—	Bpos on target (stun); Bpoc on caster (damage amp, not stunned)
Dur/HeroDur	4.5	—	channel length; successful expiry performs the takeover

Bpoc must not set ent->stunned: spell_run_frame cancels any channel on stun, and an external Bstu is what aborts Possession. Caster lock is the normal AB_CHANNEL origin/move cancel. Target Bpos is a real stun status.

On abort (caster death/stun/move, target death, cancel): strip Bpos/Bpoc, restore prior target invulnerability, no ownership change. On success: strip buffs, transfer s.player, kill the caster body.

Data Flow

AbilityData.slk (Apos / ACps / Aps2)
  -> targs, Cost, Rng, Dur, DataA-D, BuffID
CAbilityPossession / CAbilityPossessionTwo
  -> A_VALIDATE: nonhero + DataA level (+ enemy/neutral)
  -> A_EXECUTE Apos: G_SetUnitPlayer + unit_die(caster)
  -> A_EXECUTE Aps2: channel thinker, Bpos/Bpoc, optional invuln
S_ResolveAttackHit
  -> S_PossessionDamageTaken multiplies by Bpoc.data (DataB * 1000)
S_UnitSpellImmune
  -> Bpos with DataD flag blocks further spells on the victim

Diagnostic Workflow

build/bin/ability_audit -data 'data/Warcraft III' -raw Apos
build/bin/ability_audit -data 'data/Warcraft III' -raw Aps2
build/bin/ability_audit -data 'data/Warcraft III' -raw ACps

Registry rows (for s_skills.c)

{ "Apos", CAbilityPossession, AB_SPELL, SPELL_TARGET_UNIT },
{ "ACps", CAbilityPossession, AB_SPELL, SPELL_TARGET_UNIT },
{ "Aps2", CAbilityPossessionTwo, AB_SPELL | AB_CHANNEL, SPELL_TARGET_UNIT },

Verification

make test-wc3-engine WC3_PATTERN='wc3_spell.possession*'

Focused tests cover alias/procedure lookup, targs rejects without mana spend, authored DataA gate, instant takeover + caster death, Aps2 channel success and abort, DataB attack amp, and DataC invulnerability during the channel.