Moonstone Eulogist

Creature — Bat Warlock

Flying

Whenever a creature an opponent controls dies, you create a Blood token. (It's an artifact with " , , Discard a card, Sacrifice this token: Draw a card.")

Whenever you sacrifice an artifact, put a +1/+1 counter on this creature and you gain 1 life.

If an effect refers to a Blood token, it means any artifact token with the subtype Blood, even if it has gained other subtypes.
You can't sacrifice a Blood token to pay multiple costs.
Some triggered abilities trigger "whenever you sacrifice a Blood token." These abilities trigger regardless of why you sacrificed that Blood token.
If Moonstone Eulogist and one or more creatures opponents control die at the same time, its second ability will trigger for each of those creatures opponents controlled that died.