This is for D&D 5e, but any idea helps!

One of the PCs in my game sold their soul to a fiend cult to get the power they need to rescue another PC that they are super dedicated to. This dedication is one of the character's key traits, along with fear of being abandoned and a need to prove themselves. They're very self sacrificing, but also overprotective of their object of affection to the point that they disregard the person's actual feelings, like a stalker.

Currently, the other PC that they're trying to rescue has been kidnapped to the BBEG's lair, far far away.

I want to give them a few class features or special abilities to represent the pact they have. I've looked through the Warlock stuff but they aren't quite fitting.

Do you guys have any ideas of things that could fit the theme of the character?

I ended up with a lean in my soul with a character I played from first to 12th.  

I got an orb of darkness, a quill, and a Dagger of very bad.  People I killed (assinated?) with it were immediately raised as undead.

There was no mechanical down side, this was a DM that challenged us by giving us what we wanted.  He got stat boosts, over time as well.  He got a bit attack and was about to get wings (which I was going to have the dwarven cleric cut off) I think he got dark vision, and had the flat dead eyes of a serpent (snake deamoness had the lean).

Basicly I was slowly becoming a deamon, I was starting to scare the other players.  

It would only work in a long term game.  But it was cool as hell in that one.

Fiend Pact sounds like an awesome metal band.

When I first read this I thought it said "Friend Pact". That would be very different.

Quote from: RPGPundit;1009411When I first read this I thought it said "Friend Pact". That would be very different.

That'd be a children's cartoon about cute talking forest animals, I think. Based on a line of toys.

Or something like a magical oath of blood-brotherhood.