Aside from the obvious "he's gonna have command grabs", there's a few things that need to be considered for how a true grappler like Incineroar would work.
For starters, Incineroar's mobility would take a hit for the sake of balance. Not saying he'd be the slowest, just slow enough so that moving around the stage becomes a problem. Because if a grappler ends up as mobile as Diddy or Sheik, it's gonna be horribly unbalanced. Alternatively, his frame data would take the hit while his mobility gets to be decent due to movement mattering so much in a platform fighter. Either way, you can't use him as a rushdown.
Then, his combo game would be minimal. Some bread and butter stuff, maybe a few things that can be followed up by a grab to showcase that grapplers are all about grabs too? Though with a lower combo ability comes the ability to hit like a truck to compensate, especially the grabs. This, much like the above, is to avoid having a grappler used aggressively since this archetype is usually more about patience.
And also, the grabs themselves. Basically, Incineroar could have a few command grabs in his specials. He would probably lack a combo throw (and if he does have one, it's going to be a very basic "bread and butter" thing), but his throws, including the normal ones, would deal a good chunk of damage and knockback. They would likely be his most reliable kill moves and ways to rack up damage too since grabs are the best thing for a grappler.
tl;dr a grappler would likely have these things in Smash
- Either low mobility or poor frame data to avoid aggressive playstyles and encourage a more patient, bait-and-punish approach.
- Poor combo ability, but high damage output in general to once again discourage an aggressive playstyle.
- A set of powerful, highly-damaging throws and command grabs as his most reliable ways to rack up damage and get KOs.