In the early days of Banpresto before they are really famous for their SRW series, they made crossover series which involve Gundam, Kamen Rider and Ultraman in Super-Deformed game series called "The Great Battle" which most of them seen released on Super Nintendo platform. When i was a kid i used to play the 6th installment of the game on Playstation alot and it was my gateway game to Gundam series. I am quite surprised how childhood can make something biased so much since i used to think this game was the best one ever. Nevertheless Great Battle VI is still kinda decent Sidescroller.
In this game you have 3 different playable series representing their series from Gundam Wing to Ultraman. Each characters have different traits in the game with Gundam Wing being the ranged character, while Kamen Rider Black RX is the all rounder guy while Ultraman is the close range guy. The game comes in episodic formula which you can change your character on each episodes.
The premise of this game is about 3 Heroes summoned by to fight the big bad guys which is quite a staple in Japan. In Great Battle VI Wing Gundam, Kamen Rider Black RX and Ultraman team up together as Optical Three fighting against their rivals with cheesiness. At least from Gundam Side, they include MS from V Gundam and G Gundam for some reasons with Skull Gundam playing Red Skeleton role in this game.
Great Battle VI was very simple side scrolling game to be honest which are comparable with the side-scrolling SD gundam games on Nintendo platforms. Nevertheless it got multiple genre slapped in one game which is good gaming formula if underused. Few years ago there was Great Battle series on PSP called Great Battle Fullblast which i should give a try one of these days.