[@Lmpkio] Okay, then I'm going to say that yeah others can use them, but I might need to elaborate further on how they appear.

I might replace the ability with the "Aura of Doom", which means anyone within proximity of Doomguy (say fifty feet?), risks their soul becoming transformed into a power up on death. That way, it's localised and stops Godmodding, and doesn't mean that Doomguy has an entourage of people following closely behind so that they could ninja his hard earned trapped souls. Handy in a close quaters mayhem (such as the Classic Doom games are designed), but useless in strategic warfare. 

How's that sound?