Obviously, this would be something that wouldn't even be looked at now. I imagine it wouldn't be considered until the game is almost finished, but I really just wanted to leave my ideas here now. I hope that's alright. Also, I just want to say this has been a fantastic game so far, so to you all at Larian Studios; you're awesome!
I'll give achievements names, but I'm not known for being good at naming things.
Most of my ideas are for the Nautiloid in Hell.
Friends who need them - Create a four-person party from one computer. I don't know if you could even check for different the same IP address or multiple instances of the game running on the same computer.
I Want One - an achievement for clicking on multiple times or somehow trying to pick up or move one of those cannons on the Nautiloid. It would work better if I could click a pickup option but be stopped because it is too heavy, though I guess it is a living thing and not an object.
Thorough Aren't We? - Pick up every item, Chest, and Nautiloid tank, loot every corpse.
Not how we make friends - Fail every check to free the Intellect Devourer until only destroy and leave remain, choose destroy.
I'm helping. - Heal or buff the Mindflayer.
For Zareal - Heal or buff the Cambion
How? - Killing the Three Cambions and the Mindflayer before connecting the transponder. Would the Mindflayer have to turn hostile first?
I thought you had wings. - Pushing an imp off the ship, even funnier/crueler if it was the injured one.
Me and Mine - Don't talk to anyone but Lae'zel and the Mindflayer before connecting the transponder.
I'll just put this back - put the rock back over the Harper's chest.
"Animal Handling" - Kill a non-hostile animal. Why because you are apparently truly evil.
There were other ways - Attacking Kagha when the option appears the first time you meet her.
What happened?!?! - Die to the necrosis emitting from Gale's corpse
Free Service - Pickpocket the talkative skeleton.
Weeee! - Jump to your death by jumping into any hole. I'm personally thinking of the cave by the Gnoll Warlord that is attacking two guys. The one that the talkative skeleton will suddenly appear at to resurrect the foolish adventurer.