Attacks, defined by AttackData assets, can apply more than simple damage.
Actions can be performed before and after an attack by using attack effects. Additionally, these can have a specific probability of happening.
There are some existing AttackEffect classes but you can create your own by extending the AttackEffect class.
Sometime you might want a set of effects to happen with the same probability, for example if A happens then B should also happen.
For this, you can use an AttackEffectSet which is simply a list of AttackEffects. This can be used normally on an attack type as shown above with AttackEffect_Poison.
AttackEffectSet can be created from: Create→Horror Engine→Combat→Effects→Effect Set