I posted my success with Wario on GameFAQs:
Yesterday I cleared the "KO Rival 4 times" and "Score 85 KOs" at the same time using Wario. Whatever reason, it's not that hard to kill Wario, although it did help that he SD'd on the run.
- Yes I used the bike. No I didn't use it all the time.
- A mix of Side Tilts, Side Smash, and pummeling does really well against everyone.
- When you see a good few of them on the floor, one or two sweeps with the bike will do. Dismount and let the bike roll off stage
- Don't fret if CPU Wario bikes. Either avoid or an FAir to kick him off.
- The occasional UAirs when Wario or Miis are above you is helpful.
- After you've taken roughly 60% damage, NAir will become a surefire kill against Miis. Use often.
- Occasional Down Smashes to clear away enemies. Don't abuse it though
- DAir is generally useless. Only toss it out if you're comfortable with it
- Again, Side Smash. It's probably the best way to finish off CPU Wario once he's taken enough damage. It's really strong. There's also...
- ...The Waft as an option. Don't pursue the CPU just to use it though. An opening will present itself in time.
- CPU Wario WILL Waft as well however. Just stay wary of it until he lets loose.
- POW Block: Use it. Free KOs and damage on the CPU.
- Ray Gun : Use it. Same reason as POW Block
- Smart Bomb: In other Multi-Man's, I tend to avoid this. Here, you should use it. Just make sure it doesn't blow up too close to you
- Turret: I typically ignore this one. It's little more than a stalling tool, but use it if you feel compelled.
So basically your focus will be on taking out Miis while getting in potshots on Wario here and there. There's not much need to focus exclusively on him. You're also risking accumulating damage faster by directly challenging the CPU. What really works for this is that Wario is heavy, but he hits hard enough that it won't be a problem against the CPU. And unlike a character like CPU Ganondorf, the CPU Wario isn't a serious threat to you or your score. I was all the way around 240% before I finally went down to an attack from the CPU.
Play it calm, rack up the KOs, get your hits in on the CPU and land the necessary finishing blows. It also wouldn't hurt to gimp him if you can find an opportunity. CPU Wario will use the bike to recover though. There is the possibility of kicking the CPU off its bike then letting it sit there and gimping it that way. I didn't do that myself though.