Several ideas...
I was thinking it would be neat if there was a practice mode, that could be clicked within a game, ava, 2v2, coop, etc, where when clicked, skill and exp were blocked, so that there is no gain or loss. This way if I want to practice with someone, as much as I want, I don't have to worry about losing anything, and vice versa for them.
This wont be forced on anyone, for if you see it clicked, you simply don't have to play.
2.
Also, another idea, a solo mode where you are against AI, but not survivor mode, but similar to facing a person, but with different levels. Easy, normal, hard, extreme, and pros can program it. Easy does not have combos, hard uses most combos, extreme uses very advanced combos, with amazing AI, also sells towers to send big, minimum defense, etc.
3.
When in game, or spec, and when your friends come online, in the message box it will read "Michael Jackson is Online." And you can click on their name to speak to them, if you don't recall how to spell it. Might want to add an additional option in Options to disable/enable this feature.
4.
An ignore feature, to ignore messages from people. The ability to unblock them afterwards for any reason too.