The Spectrobes trilogy featuring my nigga Spikan. It's a 3D monster fightan game, except the battles are real time not turn based and you control two monsters at once. The Spectrobes themselves have different abilities and combat styles that complement each other in unique ways. There are marked gameplay differences between each installment, with the third one being a complete overhaul of the original formula. It's also the worst entry and the one which killed the series.
All in all its a strong concept that was unfortunately held back by awkward handheld controls and confusing level design.
Also If you want the first game to be a cakewalk you can grind the low level Samukabu you get near the starting area to get Samugeki, a tank form with heals, status, and ranged damage that will carry you to the final boss.
Naguzoro is another early pickup which has a retardedly strong fireball special that eats up only one bar of CH and will one shot everything until the midgame.
Finally Dongiga can spam a fuckhuge slow magma ball which deals constant damage to anything touching it and can stunlock enemies as it drags them across the battlefield with its weak knockback.