Very unlikely we’ll ever get him but the recent announcement of a New Mutants film made me think he would work quite well in this game.
Rarity: 3* - 8880 health at full level.
Blast Field (7AP) - When Cannonball reaches full speed he creates an impenetrable field that he can manipulate. Create a 2 turn countdown tile, while this tile is in play Cannonball cannot take damage from powers (can still take damage from tile matches). At 5 covers, Cannonball manipulates his field to cover the entire team, and the countdown lasts for 6 turns.
(If this is too OP, then it could just reduce damage taken like Colossus’ yellow or if it’s too underpowered it could shield from all damage, or even more-so it could even act like Invisible Woman’s invisibility tile.)
Somebody Stop Me! (13AP) Cannonball reaches uncontrollable speeds and uses his superhuman durability to smash into his opponent, destroying a random 3x3 block of tiles and dealing 430 damage. At 5 covers/maxed, Cannonball deals 5523 damage to the target, but also does 893 damage to himself (alternatively could stun himself for 2 turns rather than deal damage). If a Blast Field countdown tile is in play, he does not receive damaged/get stunned.
(The numbers need a bit of work but I like the idea)
Rocket-Man (Passive) Cannonball is able to absorb kinetic energy from his opponent. If Cannonball is damaged for more than 5% of his total health, he absorbs some of this energy and converts it into 1 yellow AP. At 5 covers, generates 3 Yellow AP and 1 Red when dealt 10% damage.
(Again, numbers definitely need work. Similar to Captain Marvel’s Energy Absorption but less powerful because Cannonball’s other attacks can do more damage).