In single player, there's an achievement for fusing Torso / Weapon / Legs to power level 8. I have done all 3 but did not get the achievement reward.

Bump.

Fusing to pwr lvl 3 achievements are also bugged (unable to be completed)

if you fused any of it while in the multiplayer screen, even if you finished the fusion in single player, the system becomes very confused and does not consider it a single player acheivement.

be sure to do all the fusing in campaign mode next time.

You have to fuse them to power lvl 9. They are Because once they pass the whole power lvl of 8 then goes lvl 9. Exp:

Cannon Feet:

power lvl 0: 0- 150

power lvl 1: 150 - 300

power lvl 2: 300 - 600

power lvl 3: 600 - 1200

Basically you have to pass the lvl gap. So If your torso, weapon, and leg still 8, then get it to lvl 9.

I assumed they knew that much, but in the past I have had issues with the fusion acheivment because I'd fused part of it in the multiplayer lobby

Thanx all for clarifications. Started playing just a several days ago and did not know that.
I assumed that achievement requiring you to fuse part to pwr lvl 3 would be completed once you fuse a part to the point where it says "power level: 3"
But you're saying it should say "power level: 4"

So... this is not a bug, but more like an errata in the achievement.

Thanx once again.

I know this is irrelevant but a tip for this achievement:
Fuse into newbie torso, then into whatever cheap weapon or legs you have, then finally into the item you want to have fusion. With enough power you can clear the achievements in one go