ICs are somewhat difficult to use because higher level play revolves around desyncs, which are difficult to pull off and even harder to use efficiently. Their skill curve is kinda steep. But I don't play ICs so my advice comes from reading around and watching other players.
Wario is just insane. While he's not usually top tier in P:M, he has plenty of weird tools to keep opponents confused. He has among the best aerial mobility in the game, able to weave from side to side in the air and keep them guessing as to how you'll approach. His new Back aerial is a slow punch behind him with good KO power, and his down aerial is now a ground pound that sets up combos and meteor smashes opponents.
He also has a great killing tool in his new Side B, the Shoulder Bash. It gets stronger the longer it's out on the ground and you can jump once while keeping the attack out. If you fall off of a platform in Shoulder Bash and jump in midair during the bash, you conserve your double jump, which is great for mixups. It's best used sparingly for reads since it's laggy, especially if it hits a shield, and locks you into predictable directions until the attack ends. However, it's much stronger than at first glance, so it is unwise to dismiss it.
Wario got other changes to his moveset from Brawl as well: Down Smash is now a short range ground pound that spikes opponents towards the ground. It also hits offstage if you're close enough to the edge, making it difficult but rewarding as an edgeguarding tool. If onstage and they don't tech, they are susceptible to another Down Smash or, if you get a read, either a Shoulder Bash or Wario's new Forward Smash. Fsmash is a very sudden kick with a bit of endlag to compensate for it's decent power.
Wario's Forward and Back throws also got changes. Forward throw is a chargeable toss forward, the uncharged great for starting combos and the fully charged a decent killing tool at high percents. Back throw is now a spinning toss, same as Mario and Luigi, but you're able to move side to side while doing the spin. You can either move towards the edge to toss them farther out or away in order to confuse players who don't know the matchup or otherwise gain a positional advantage onstage.
Wario's Forward Tilt is also great: its power is good and it is pseudo-chargeable. By holding A down Wario doesn't attack for a total of 30 frames, it's damage and knockback slightly increasing as it's held. It's great for mixups, as it is difficult to tell when Wario will actually punch if he doesn't decide to fully charge it.
Don't forget Down B! Wario Waft now fully charges faster but does much less damage and knockback. However, it is still an awesome surprise tool, as it KOs at higher percents and Wario's body becomes its own hitbox while he rises. The lower charge time and the ability to conserve charge between stocks is also useful as it can aid in Wario's not-so-stellar recovery.
