I'm having a really big issue with ROB and Diddy Kong. I play Mac and I'm a bit lazy to find any source on how to deal with the MU. Can anyone help me out?
Not really knowledgeable here because I don't actually know the character vs Mac that well, although I know some basic stuff that'll probably help.
If the Gyro is on the ground, grab it. Its so amazing. Z-Drops bounce them a really low and short distance into a Rising Uppercut or Up Smash, and cover ledge getups. If you throw it up its a zoning tool that has an unpredictable landing time. Down and both side directions are just for direct hits. It will disappear after 1 hit unless you grab it before it hits the ground, so remember that.
His KO options are Up Smash, Forward Smash closest to R.O.B.'s body, Up Air, and Up Throw. If he throws you offstage with Fthrow or BThrow he also can get KOs with lasers to gimp or Forward Airs to gimp as well. Neutral Air at high %s can KO but its really unlikely. Up Smash is rare since while its a great option it isn't true out of anything barring a Gyro Z-Drop, which even then can be shielded unless you get hard read. Forward Smash is incredibly weak far from R.O.B. and is probably the second worst FSmash for doing that job at the sourspot. Up Air is a kill confirm off a Down Throw but if you DI properly (which is very hard to do) you can live to long percents. Up Throw KOs off platforms pretty easily but on the ground just DI away and you are fine.
R.O.B. struggles against Super Armor and losing his Gyro; if he can't do his normal tools he has to rely on zoning with Lasers which isn't very much a great plan as they have a recharge time. His large hitbox also makes him weak to Up Tilt and Down Tilt combos, so just keep linking those and you are good. Jab won't do much since he won't be hitting right in front of you or landing in front of you often - same goes for Forward Tilt, but it is a KO option. His recovery also is basically impossible to gimp due to how good his Up Special is, so avoid using Down Smash but instead avoid an Up Air or an off-ledge Forward Air.
Personally Diddy is one of my harder fight-against characters since I suck against any form of aggression, but Diddy isn't too bad. If you get hit by a banana, prepare to DI for a Down/Up Throw Up Air or if you are at around 60-70% DI in for a Back/Forward Throw near the ledge. Banana is really key since whoever has access to it immediately has control of the match; Diddy can get Up Smash, Forward Smash, and a Grab off it, while you can get a Running Up Smash or Grab since nothing else has enough reward to warrant using. Diddy's lightweightyness makes him relatively easy to KO, but the fact his recovery is extremely long reaching and has two parts for horizontal recovery makes him harder than R.O.B. by a long shot (Personally I have it as a 55/45, Diddy's favor).
If Diddy has the banana, Jab. Jab clashes with Banana and you transition into Jab 2, then back to Jab 1. It also stuffs most of Diddy's approaches. If he's readying to get a banana, go aggressive and force him to not get it or space you out with a Fair or Nair - dash shield if you can and then punish. If the Banana is on the ground, Down Tilt will instantly destroy the Banana and cause Diddy to have to get another. If you see they are retreating from the on-ground Banana, Dash Attack to grab it or jump and airdodge right before landing to grab it. Basically, don't let Diddy have the banana.
If in the neutral and he's spamming Peanut Popgun, don't approach or fall for any of his bull****. He's just waiting for you to approach. If anything this gives you a free opportunity to practice Powershielding. At low %s he can Down Throw Bair BAir, but don't freak out over it because this is basically normal stuff. Just DI in. At high %s he will try being risky to get the KO, and at this point if you have a KO Punch call him out on an approach with constant dash shielding and spotdodges or FSmash him if necessary.
