Underrealm Lich has the ability Prevent Damage and “Whenever this creature prevents damage, it loses Prevent Damage for 2 turns and you lose 4 life.”
This second ability is improperly triggering when it is being dealt 0 damage. For example, when it attacks into an 0/4 plant token created by Dowsing Dagger, it is not being dealt damage from the plant token. However, it loses Prevent Damage and deals 4 damage whenever it attacks into the 0 power creature, which shouldn’t happen.