HA! is an attack special designed by Kleya Smith. She planned on using it in the DeathMatch, but was unable to use it. The Bandit used his special and was able to bring her down below 5 HP, so she found out too late that she can't use an attack special under 5 HP.
We have yet to see what it does. The only thing we know about it is that Kleya thought it could defeat The Bandit in the DeathMatch, but she still opted to make another more effective special for the Game Trials.