This suggestion might seem strange, but I think Charlie the Unicorn might be a good character. "Charlie the Unicorn" is a popular movie, with over a million views and a score of 4.31. The big attraction is that Charlie, as a quadruped, would feel different than all of the other characters. It is important that each character is unique and fun to play, which I am sure Charlie the Unicorn would be. Do not think that he would be a wimp; anyone who has seen a bucking bronco will tell you that their kicks are deadly. That horn would be another dangerous weapon. He could even use his tail as a weapon. There was even a flash movie called "Charlie the Unicombat" that featured Charlie the Unicorn killing other unicorns in a madness style.
I think a cool attack would be one in which Charlie impales the opponent on his horn, then throws him back and kicks him on the way down. Another attack could be Charlie bouncing an opponent on his head the way that Bitey bounced that little yellow farty thing (name?) in "Bitey of Brackenwood." With that horn, an attack like that could really hurt.
I do not know what the projectile could be. The only thing I can think of is horse shoes. Charlie would kick, and horse shoes would fly off.
A Charlie the Unicorn themed arena could be in the forest, with the magical Liopleurodon on one side and Candy Mountain on the other as platforms. You could include the other two unicorns in the background if you wanted.
I could think of several storylines. First, Charlie could be out to find his stolen kidney (from "Charlie the Unicorn). In this storyline, an arena with Candy Mountain would be particularly useful for the first or last battle. If you adopt this storyline, you should animate Charlie with either a scar or bandages from when his kidney was stolen. Second, Charlie could be driven mad by the other two unicorns and go on a killing spree. Third, Charlie could be pressured by the other two unicorns to become the king of Newgrounds, the way they pressured him into going to Candy Mountain in the first episode and finding the Banana King in the second episode. Personally, I like the first idea best.
Charlie the Unicorn http://www.newgrounds.com/portal/view/28 0260
Charlie the Unicorn 2 http://www.newgrounds.com/portal/view/43 5202
Charlie the Unicombat http://www.newgrounds.com/portal/view/40 3323
That is all that I can think of about Charlie the Unicorn. I hope the authors find my suggestion useful, and that everyone else finds it interesting. Please post your own suggestions and critique mine. Thank you.