[quote=@Saint Girralo]
Second question regarding Doom Guy. Does Doom Guy have to kill them himself for the power-up to drop or can anyone kill them and cause it to drop?
[/quote]

Updated the ability. Now anyone who dies within fifty feet of him (barring some exceptions, such as important NPC/characters/plot related fluff) has a small chance to have their soul trapped as a power up. So, that goes for enemies and goodies. Whoever dies in that radius might become a power up, to be used by anyone who touches it. 

It's as beautiful as it is chaotic.