Bahamutt is a colossal dragon encountered by Mario and his allies while exploring Bowser's Keep in Super Mario RPG: Legend of the Seven Stars. Both Chester and Magikoopa can summon him to help them in battle, as he is indeed a powerful foe. Bahamutt has a lot of HP and above average stats. Besides regular biting attacks, the dragon can resort to the special moves Iron Maiden, which triggers a Fear status ailment, and Drain.
Despite being very strong, Bahamutt doesn't seem very confident in his own abilities, as revealed by his Psychopath thought. (Credit given to mariowiki: http://www.mariowiki.com/Bahamutt)
In Flashbolt's adventures
Bahamutt's first appearance in pokemon universe after more years than his absence was in a episode called "Bahamutt's first stop!" which Flashbolt and his allies tries to explore into Grondice's castle, but unfortunately for them, they had encountered him, and he blocks their way. So the battle starts until Flashbolt and his allies defeated him. He scared away from Flashbolt and his allies into an unknown area. He was never seen again until a sequel episode revealed that he running into an unknown area that is Pokemon village thus attacking many pokemon. unlike Bahamutt's first stop, he is voiced by Yoshi's voice actor but with more masculine dialouges.