Multi-school abilities benefit from bonuses that affect any of their schools, use the lowest resistance value among their schools, ignore absorption and immunity effects that apply to only some of their schools, and can be used even when one or more of their schools have been locked with an interrupt effect.
Chaos's nature guarantees that damage done will not be mitigated by any armor, resistances or school-specific effects the target might possess. However, mitigation and immunity abilities that are not school-specific (such as [Ice Block] and [Divine Shield]) as well as damage-absorption shields provide by abilities like [Mastery: Blood Shield] and [Power Word: Shield] will still absorb, mitigate or completely prevent damage from this school. Due to its comprehensive nature, it is impossible for players to be locked out of the Chaos school unless a Chaos spell itself is interrupted, in which case spells of all included schools will be locked out.
[Ice Block] and 
[Divine Shield]) as well as damage-absorption shields provide by abilities like 
[Mastery: Blood Shield] and 
[Power Word: Shield] will still absorb, mitigate or completely prevent damage from this school. Due to its comprehensive nature, it is impossible for players to be locked out of the Chaos school unless a Chaos spell itself is interrupted, in which case spells of all included schools will be locked out.
[Annihilation]
[Chaos Nova]
[Chaos Strike]
[Disrupt]
[Eye Beam]
[Essence Break]
[Fel Barrage]
[Fel Eruption]
[Fel Lance]
[Fel Rush]
[Glaive Tempest]
[Fury of the Illidari]
[Mana Break]
[Mana Rift]
[Chaos Bolt]
[Chaos Wave]
[Dimensional Rift]
[Any Means Necessary] turns any Arcane, Fire, Frost, Nature, and Shadow damage they deal into Chaos damage, this includes 
