1)There are graves when enemy becomes dead -I don`t like this that all and I hope it`s placeholder or temporary desighner`s decision
I do not remember where I read this, but the explanation for the graves seems to be the following:
The gravestones appear only if the enemies are killed by magic and not by conventional attacks like stabbing, shooting, etc. The enemies killed by magic can be resurrected by other enemies and therefore there needs to be some kind of an indicator where a potentially undead creature is lying.