Well we know it's going to somehow be in the game:

Atlantis, with the ocean in the background

Aquaman - can summon a tsunami and summon different sea creatures at once for a jubilee-attack

Black Canary - grab a conch shell and blow into it making a sonic boom that stuns the opponent

Poison Ivy - cause coconuts to fall out of a tree onto opponents head, then she summons a vine from the branches, swings and beautifully kicks the opponent like she's a dancer

Red Tornado - make a dirt-devil out of the sand/sea shells and make a waterspout

Captain Cold - makes an iceburg out of a regular wave that just keeps rolling twards opponent until it hits them

Catwoman - if hit with water of any kind it makes her more powerful/p!$$ed off.

Hawkman - does a dive into the water, comes out with a huge clam shell and drops it on the opponent

Zatanna - knock the opponent in the water, then summon a lighting bolt

Mirrorman - utilizes the sun in which reflects an energyblast at the opponent

Batman - summons the batboat

Plasticman - resembles the Lock Ness Monster in the water with a lunge attack

I think the Fortress of Solitude will have snow balls.