From what I've been able to gather, you can do tag specials with any character that will be in the game. Not everyone will be able to be included (I think the limit is around 48), but Juan's compiling a list of these characters that he'll post before long.
A list of all the available characters? Now that would be useful. Also, is it just me failing at searching or are some of those characters Juan mentioned lacking profiles?
And how's this for a moveset in progress?
1 - Mystic "Power of the Four Elements" (special ability) = This move has Imagni use his limited abilities of elemental magic. He concentrates for a moment, and then fires a small orb of magical energy at the opponent. The orb randomly has one of four effects: temporarily setting the opponent on fire, freezing him for a short while, knocking him off his feet with a small earth tremor, or getting him off-balance with a gust of wind.
2 - Ballistics [haven't come up with a subtitle for this attack yet] (weapon) = Imagni takes out a small remote control from his pocket and presses a button, firing the four large cannons hovering just behind the battlefield, and then moving them to the next alignment in a cycle of four (corners, middle, horizontal row along the ground, and cross formation around the middle). The attack has a cooldown time of five seconds; if it is used during that period, the cannons will simply move to the next position without firing.
3 - Classic Mechanics "Gravity" (projectile-based special) = Imagni positions his fortress right above the battlefield, and has it drop down a mass of cannonballs on the spot where he was when the move was activated. The move takes about five seconds to start from that it is performed, but Imagni is free to move and use other attacks (though not ones involving the fortress, for obvious reasons) during that time.
4 - Number Theory "Approximating Pi" (what attack category would this be?) = A small laser is fired from the fortress, and proceeds to trace a circle around the opponent, leaving a glowing (but non-damaging) trail. Once the laser has gone the whole way around (which takes about a second), four other lasers appear, quickly tracing four diameters across the circle. Then, Imagni fires a big beam from the Reactor, completely covering the circle. In short, you do not wish to remain inside the circle once it is completed.