Well, I've noticed something about most R.O.B. users. They like to start off the match with a Laser. When starting, try spot-dodging immediately.This will make the laser they launched fly harmlessly past you.
Always pay attention to when his laser is ready to be launched and when you are vulnerable. Spot-dodge and air-dodge often to avoid getting hit by it or a ricochet shot.
Don't chain-grab when a gyromite is out. DON'T DO IT. A simple D-Throw to F-Tilt should be enough to get some damage in on them and disrupt them. And when they charge it up, that is your warning. From that point on, you know that it can be launched at any point. Again, air-dodging and spot-dodging come in handy. Also, approaching in the air with either a D-air or B-air help avoid getting hit with it on the ground. Approaching with D-Air helps rack up damage quickly. However, you have to worry about R.O.B.'s U-smash, which comes out fast and hits hard. Your safest bet is B-Air approach.
And as for his D-Smash, try keeping him out of range with an F-Tilt, D-Tilt, or B-Air. Also, using Dedede's amazing air-game helps avoid his D-Smash. You just have to worry about his U-smash when in the air.
And try not to use Dedede's Inhale move as anything more than a situational edge-guard. His Inhale only leaves you vulnerable due to the amount of lag the move has to begin and to end.
Also, worry about R.O.B.'s N-Air. It is a huge pain and completely protects R.O.B. from all around. However, it leaves him vulnerable directly after the move is finished. As soon as the move is finished, hit him with a B-Air. Beware edge-guarding an experienced R.O.B. user.
However, all of my advice could be useless garbage. I've only faced a few good R.O.B. users and those all helped me fend them off.
I hope it helped.
