Just finished getting all achievements for Thing Thing and PD, decided not to go too far in Alkie Kong unless SUPER bored because the achievements I don't have are (gulp) hard.
So pretty much, the only Thing Thing achievements that drove me nutso was Proxy Mine, given the lack of ammo.
The rebound shotgun only needs a small cave and the gun pointed at the ceiling for max effect.
The acid grenade requires TONS of ammo (have it as a secondary while getting 100 with another weapon to get the ammo for acid really high) then stay next to a wall somewhat near a spawn point and shoot indiscriminately in the same spot for a potent and constant dose. Actually one of the easiest.
The best way for headshots were the Dart Grenade and any of the shotguns.
As for Portal Defenders, Bob means you can do no bombs and no organs (I got both in one go as Bob) and he's also great for Horde killing if you restrain yourself against Wade. The only one that really bugged me was ZOMBIIEEEZ because it's solely based on luck: it took me FOREVER to spawn five brains. I got it as April under the theory that combos yield more organs, but I might just be crazy.
But yeah, loving the medals, but hate it when it's solely based on luck. Even in Alkie Kong, with the super impossible achievements later on, is still based on skills rather than pure luck. Otherwise, great system, NG! Hopefully Newgrounds Rumble and some Fulpadin classics can get in on the action. Also, I'd love for there to be a rankings so that us nerds/bored people can compare scores and the completely meaningless internet points Medals give can become a completely meaningless competition.
Love ya, Newgrounds.