Let us begin R.O.B as you may know is a Nes accessory and he debuted in Smash Bros Brawl so let's go move by move and go over the different combos each move can do.
Jab at low percents dosen't combo to much but can Jab Lock which is very useful for R.O.B especially because it can result in a Side b punish
At Mid percents it can maybe result in a nair but that can be air dodged pretty easily so not much
At High percentages it has nothing notable
For Uptilt at low percentages it's a fine damage move dosen't combo into anything noteworthy
At Mid percents it can combo into nair and sometimes Side b but that's reactivable
At High Percentages is the same as Mid except the nair is more reactivable
For Down Tilt it's a fine poking rool all across the board no real combos or anything
For Forward tilt at low Percents it can help set up the 0 to death combo that involves using your Down B and repeatedly throwing and catching it with nair and finishing with the side b it can also lead to full charged Neutral b into a side b and if timed correctly it can lead into a Forward smash.
At Mid percents it can do the same thing as low except the Neutral b into side becomes sheldable
At high it loses the nair and Down b juggling ability but it gains the ability to knock most characters a reasonable amount of the ledge with can lead to bairs and nairs and of course dair spikes
For Down throw it leads to uairs and nair consistently at all percentages
For Forward throw it can get most characters a reasonable amount of stage but only at ledge it's a discount forward tilt through out all percentages
For Up throw see Down throw but this can kill in mid to late hundreds on top battlefield platform it's pretty pretty rare that it matters but it has come in clutch once or twice for me
For Back throw it's literally Forward throw but behind you
For Nair with every combo with nair i have talked about there is also nair carrying off stage for characters with weak recoveries and is involved with that 0 to death combo I have talked about and sometimes Nair can combo into a well placed midair Side b
For Dair it spikes of stage that's its purpose if you get a spike on stage it can lead to uair
For Bair it doesn't have a lot of combos it can combo from forward tilt and throw but it's purpose is mainly as a egegareding rool
For Uair it can combo from Up throw and Down throw and is very good at catching air dodge's
For Fair it is Forward Tilt/Throw but this time it's in the air and it is a decent combo extender and can combo into nair and Side B
For Up B Doesn't have a hitbox
For Side B has the 0 to death combo and has the jab lock along others that have already been mentioned
For Neutral B has the side B combo and can lead into an Forward smash Down smash or Up
smash
For Down B has the 0 to death combo and it can also lead into a Side B and Side smash
For Smash attacks only one smash attack being forward smash really has combos being a great combo extender and having so much range it can combo into Side B and nair and even uair sometimes
So this took a few hours to make so I hope it helps
Jab at low percents dosen't combo to much but can Jab Lock which is very useful for R.O.B especially because it can result in a Side b punish
At Mid percents it can maybe result in a nair but that can be air dodged pretty easily so not much
At High percentages it has nothing notable
For Uptilt at low percentages it's a fine damage move dosen't combo into anything noteworthy
At Mid percents it can combo into nair and sometimes Side b but that's reactivable
At High Percentages is the same as Mid except the nair is more reactivable
For Down Tilt it's a fine poking rool all across the board no real combos or anything
For Forward tilt at low Percents it can help set up the 0 to death combo that involves using your Down B and repeatedly throwing and catching it with nair and finishing with the side b it can also lead to full charged Neutral b into a side b and if timed correctly it can lead into a Forward smash.
At Mid percents it can do the same thing as low except the Neutral b into side becomes sheldable
At high it loses the nair and Down b juggling ability but it gains the ability to knock most characters a reasonable amount of the ledge with can lead to bairs and nairs and of course dair spikes
For Down throw it leads to uairs and nair consistently at all percentages
For Forward throw it can get most characters a reasonable amount of stage but only at ledge it's a discount forward tilt through out all percentages
For Up throw see Down throw but this can kill in mid to late hundreds on top battlefield platform it's pretty pretty rare that it matters but it has come in clutch once or twice for me
For Back throw it's literally Forward throw but behind you
For Nair with every combo with nair i have talked about there is also nair carrying off stage for characters with weak recoveries and is involved with that 0 to death combo I have talked about and sometimes Nair can combo into a well placed midair Side b
For Dair it spikes of stage that's its purpose if you get a spike on stage it can lead to uair
For Bair it doesn't have a lot of combos it can combo from forward tilt and throw but it's purpose is mainly as a egegareding rool
For Uair it can combo from Up throw and Down throw and is very good at catching air dodge's
For Fair it is Forward Tilt/Throw but this time it's in the air and it is a decent combo extender and can combo into nair and Side B
For Up B Doesn't have a hitbox
For Side B has the 0 to death combo and has the jab lock along others that have already been mentioned
For Neutral B has the side B combo and can lead into an Forward smash Down smash or Up
smash
For Down B has the 0 to death combo and it can also lead into a Side B and Side smash
For Smash attacks only one smash attack being forward smash really has combos being a great combo extender and having so much range it can combo into Side B and nair and even uair sometimes
So this took a few hours to make so I hope it helps