Encounter: Blood Soaked Hag and Her Pets

Surf's up, friend!

This is a concept thought up by +Tallor Daniels, which, he tells me, he gets this idea in turn from One Punch Man. It sounds interesting, and complicated, but also pretty modular.
Sorry; I'm already talking about it without saying what it is.
"It" as it so happens, is a witch who has a swarm of friends who absorb life from enemies, and using this life force, casts magic. Let's look at ways to put this together.