The speculation is that Vision is the Spec Ops 5 reward hero and Ultron is the big villain. But then that's just speculation and we've got demons to fight. Meanwhile, I'll tell you one similar rumour and the reward's attacks.
Ant Man vs Ultron
After all, Hank Pym was the one who created Ultron, right. And plus, he is more well known in the marvel universe and with a 2014 film about the man, how can Playdom resist? Ant-Man is cool, since he can turn big and turn small, which means two powers.
His attacks might be: 1. Brawl (single target)-Causes Get Big (stackable) making Ant-Man giant and increases attack by more than two times for two turns.
2.Jump Down (buff)
-Causes Get Small making Ant-Man small and flying.
-Also increases evasion by 25%.
3. Giga Stomp (single target)
-Causes Get Big
-Consumes one Get Big to do extra damage.
4. Call the ants (AOE)
-Chance to fail
-Does more damage if Ant-Man has get small
I'll make a more detailed version of it.
Agent Destructive over