I've been trying to remember this game for years. Here's what I remember for certain:
1) It's a windows platformer game released in the mid to late 90s.
2) It was available from download.com as a free game (pretty sure anyways)
3) It could be played online against other users.
4) It had the word hell, devil, satan, evil, demon or something similar in the title.
5) You played as a guy who fought against aliens and demons and you could switch bodies with the enemies.
6) The sprites were pretty small.
7) Weapons included chainsaws and guns.