forgetYEP
solo'd the Twins on a strip of hellstone
sans obsidian gear, you'll receive constant, barely noticable damage instead of the heavy damage of the terrible 2. so it's about as good as being invincible as you load them with some bullets 'til they asplod
EDIT: PROTIP: Cross Necklaces are real good to reforge, costing around 20 silver per reforge so it's easier to get a lot of prefixes without breakin' the safe.