When you fight Satan, one of the major parts of the battle is having to balance fighting him versus fending off the bats. A (relatively) simple solution to this dilemma is to (if you are ranged) sit on the bat spawn point and shoot Satan with your wand or bow and just out-heal the Ungodly Fires, which isn't too bad. If you are melee, then you just wait until a bat spawns, and then throw a net at it so that it blocks the spawn point.

A pretty good solution to this would be to enable spawning of vampire bats from two locations instead of one – the current spot and then the spot opposite it.