On the mushrooms, remember in season one, when Ragnar was badly injured, it was Floki that had the knowledge to nurse him back to health.
He doesn't live in town with the rest of them. He lives out in the woods overlooking it
I get the sense that he knows herbs and plants and such, has some rudimentary medical knowledge, and given his strange spiritual side, probably does whatever the viking equivalent of mind-altering drugs are, from time to time. He probably knew of a mushroom that knocks you out for a few hours and numbs pain. It allowed Rollo to fight a little, and knocked Torsten out to appear dead. You'd just have to time it right, and be sure to give it to Rollo a few hours ahead of time so he'd be awake, and numb, when you needed him...which is exactly what Floki did.