The third entry in the Mario & Luigi RPG series (which is a sort of counterpart to the Paper Mario games) is just about what you'd expect: a turn-based adventure that deftly combines platforming and role-playing elements. Sure, you take turns trading blows with enemies, but with good enough timing, you can avoid attack entirely or even counter-attack.
This time, though, the Mario brothers end up being sucked into the body of their nemesis, the surly Koopa king Bowser. The rest of the game unfolds as a sort of tandem tale, with the brothers fighting their way through their foe's body in order to help him become a more powerful turtle tyrant. Bowser, you see, has been deposed by the deranged magician Fawful, and he hopes to reclaim his throne. It's a strange premise for a game, but it does give developer Alpha Dream an excuse to bring back wacky fan-favorite Fawful, so all's fair.