Rogue exploit plus sneak attack

[Spatula]

Well, it'll be easier than 3rd at least. Creatures aren't immune to it

Fewer creatures are immune. There are still creatures that can't be sneak attacked. The one plant creature that's shown up in DDM stats is immune to sneak attack (verdant reaver from Night Below), and there's a couple of elementals that don't give combat advantage and thus could not be sneak attacked (fire elemental, fire archon from Desert of Desolation).

Sunrisekid, do you actually know if the backstabber feat will increase sneak attack damage to a d8? That seems pretty powerful for a feat.

It's +1 average dmg per die of SA, so I'm not sure how amazingly powerful that is... hard to say without seeing more feats.