I'm pretty sure I've seen people talk about immunity to ability damage. What sorts of stuff grant that?
Also, regarding torch bug paste, that's pretty cool(and I'll definitely be looking into getting some in my current campaign), but from it's description it wouldn't help against mirror image (at least my reading of faerie fire doesn't seem to include mirror image, since it's not actually concealment). Against a caster you're looking at 2 full rounds to deal with invisibility + mirror images(take out torch bug paste, throw it, take out acid flask, throw it). At which point, when you go to charge them, they put mirror image back up as an immediate action. So yah... still not sure why illusion bane doesn't get mentioned for beat sticks. That's a lot of action economy, which could be the difference between a clean kill, and getting bogged down in BFC.