Bowser is very greedy and constantly attempts to take over the world. Unlike his namesake he's not very interested in capturing princesses. He appears to have the ability to change in size, as during his second and third encounters he was around the size of a small skyscraper.
Bowser was first met by Tagg, Gamer, and Meddler as they traveled towards the Unova League when Palkia's hangover caused a rift in spacetime that had them traverse a Mario themed path, culminating in them defeating him. He was encountered again by Tagg, his mons, and Abigail in a giant hot-tub floating above the Orange Islands, only to fall once they'd managed to destroy all the supports holding it up. The third instance involved Tagg and Cleffa chasing him across the Dream World only to defeat him in front of a black hole.