Theoretical stuff here:
PK Flash- R.O.B can't airdodge out of his recovery :/ I don't see a single reason why PK Flash isn't useful.
Because before you realize, Rob is already back on the stage.
PK Thunder- Any character that falls slowly is a joke, from what I remember R.O.B falls pretty slowly.
From the right angle, this one is dangerous for Rob, you are not going to gimp him, but it will give him trouble landing.
PK Fire- You can basically call this move PK13370, I don't think I've ever gone a stock without using it once XD. Not saying you should use it that way, but just saying I know the move in and out. I don't really see how R.O.B could horribly punish this...He's kinda slow, but he could get a nice hit in. He's big enough that it might be hard to get out, and he'll want to be in the air so spiking him when he's in the pillar can set up a nice jab lock.
Usually if I fail to powershield, I just DI out very fast, it's hard to punish Ness, but I won't get so much damage in the process.
PSIMAG- Just for reference, jump cancel is toooo good.