Mains: Big Daddy, Sweet Tooth
Learning: Ratchet, Sir Daniel
The air downward shotgun is good for AP gain against people on the ground that won't let you hit them with the jumping square. Which any good players you're pretty much not going to get them with the jumping square so be prepared to have people say you're spamming the shotgun.
What Fat Slapper said about the jumping square combo. Jumping square, down square, and then instead of hitting down O and laying the bomb, do an uppercut in its place and then a forward shotgun. You won't have to jump into the air to hit with the forward shotgun and your bomb will still be wherever else it's at. I feel this one is a better combo because 90AP, no AP burst so no AP given away. So air triangle, down square, up square, forward triangle.
Jumping square is a hit confirm for his level one. It's a pretty quick level one so you might be able to hit someone after defending a long recovery attack as well.
Throw combo - down throw, up square, forward triangle
90 AP - neutral air square, down square, up square, forward triangle
AP burst(140 AP) - neutral air square, down square, down circle, walk forward and up circle, jump and forward triangle.
...Start combo with a jumped up triangle into your neutral air circle for 150 AP combo.
Also, if you do forward down throw I'm pretty sure and they bounch onto a platform, jump up and neutral air square ffor an easy kill.
Your lvl 1 if the BEST punisher in the game. They screw up a move that has a lot of recovery time? HIT THEM. Mess up that super? HIT THEM. Use it PERFECTLY as a counter and you'll be dangerous.