Chaotic

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Chaotic is an attribute that, among other things, makes a creature extremely susceptible to silver weapons.

Chaotic monsters

Shapeshifters, all ugly things, abominations large and small, killer klowns, Tiamat.
A creature having a mutating attack or a chaotic attack flavor (as opposed to simply having a chaos-branded weapon, like Crazy Yiuf).
A creature having an intrinsic chaotic spell, such as Mnoleg (as opposed to simply being a spellcaster with a chaotic spell, such as Kirke).