Originally posted by Lurksmore:

I have 2 fire geysers near by. Make them walk over them til they die.

This is by far the fastest way. I have a swamp zone that has half a dozen fire vents all near each other, and I just kit the abominations over them. Dead very quickly.

Also get a ton of coal, and surtling cores at the same time (this is the main reason I have a portal to this swamp, it's to farm coal).