From The Bakugan Wiki

Combos were combinations of Ability on Bakugan Dimensions. If you use an attack called a "Combo Start", then you start a combo. If you have a "Combo Continue" you can click on, that to make your attack do more damage. (Much like Fusion Abilities) But, if the opponent has a "Combo Escape", they can click on that to escape the Combo. But they lose that ability, which can be a good benefit. The only way you can start a combo is, if your opponent doesn't block your combo start attack.