Can all achievements be unlocked offline?
 

Like the two player troll kill? can it be achieved in single player or would i have to do it over live?

I think you have to do it online. That's how i got mine.

Yeah I'm pretty sure the two person troll kill is online only, but the achievement for having someone throw an enemy in the air and you kill them can be done in single player, I didnt think it could be but then it popped for me. I think all the rest are obtainable offline but having online would considerably help with collecting the peices of the elite sets trading with others here on the forum

Short answer is that the only achievement that can only be done online in Too Human is the Troll Takedown.

If you would like to partner up for this achievement, my GT is Sgt E Sanders