Gamabunta: A decent summon, more or less. He's able to use up to S-Rank water, so that's a plus. But, what I like the most is how he's immune to all Ninjutsu up to B-Rank. Good for certain fire/oil combos and he has decent sword skills.
Gamaken: The clumsy toad lol Like Gamachu, he only has Taijutsu and Kenjutsu skills. But, like Gamabunta, he has an immunity to Ninjutsu, though limited to B-Rank and under.
Gamahiro: Cool summon with a cooler way of being summoned to the battlefield. Although, his combat abilities are pretty much the same as Gamaken's — nothing too interesting.