"Zoids Battle Colosseum" was released in 2006 for the Nintendo DS. It's tied to the Zoids Card Colosseum arcade game. It has a story mode, a battle mode, and a wireless mode to battle with friends.The battle system is based on Rock, Paper, Scissors, which makes it more of a luck-based game than skill based. This makes it fairly easy to play, even if you don't know any Japanese. As you play the game, you collect battle chips of either Zoids, Pilots or Battle Chances, which you can use to create decks for battling. You can make up to four decks.
The chip system is a basic addition system. If you start with Liger Zero (8), Rakoru (6), and an E-shield (6) Battle Chance Card, you get (20) all together. If you have Bit (10), it's a total of (24). Of course the better the number, the better attack/hp stats you have, but with a luck based battle system, it would be technically possible to beat a Deathsaurer with a Molga (not that I've tried).
Each pilot has one or two Zoids they have a special connection to. When paired with that Zoid, it will power up into a special version of the Zoid, even if you don't have the chip for the powered up version.
The story starts out with Rakoru and his friends Teru and Rin. Somehow they've been pulled into the Battle Colosseum game, and must battle their way against some mysterious opponents to make their way out. Along their journey, they meet various characters from all four of the Zoids animated series, as well as a few from the Zoids Web Comic (which is sadly no longer around).
As you beat the story mode, you can unlock images for the Zi Gals Picture Encyclopedia, which is basically a bunch of illustrations of girls dressed up as Zoids. You have to beat the story mode multiple times to unlock all the images.
Official Takeratomy Site: Zoids Battle Colosseum