What was the name of this old playstation 1 game?

I don't really remember much of it as it was about 10 years ago that I use to play it. But I'm pretty sure it was a Japanese game and maybe started with 'E' it was a long word that I could never pronounce lol. Anyways, in the game you're a weird looking animal that kinda looks like pikachu and there's other characters on it that kinda look like jigglypufff lol. I mainly remember two parts of the game.. In one part you're in a mine cart and youre going through mine. And the other I remember is you're fighting the boss of one of the levels on top of a hill, the boss can swing his tail around and makes makes a wave in the ground. Im not the best at describing but I hardly remember it. I don't think it was on one of the demo discs but then again it could have been..? If anyone can help me that would be awesome!