I feel like this MU should be wayyyy in R.O.B.'s favor, but I always seem to have trouble with it when it's a good D3. Spammy, campy D3's are easy--But when they know what they're doing it can get difficult.
D3's a big tank who also happens to have 5 jumps and massive Up-B. So killing him is a nightmare half the time. He'll actually die at pretty normal percents to beep-boops, but the issue is grabbing him. His grab range is insane--Even more so if he pivot grabs. Good D3's know how to really abuse that grab, and they have good confirms off throws too--Especially on big robots.
So it can be sort of hard to know what to do. If you stay back and zone, he can too with Gordos. Albeit, they're easily hit back, but good D3's can catch them again and toss them right back. If you go in aggressive, which is obviously optimal on big, fat combo-food, it's easy to fall into that grab range and just get bodied.
I went to the Xanadu Arcadian and almost got 2nd in my bracket, but was kicked by a D3. I didn't take one stock off the whole set.