Monster Tale for the Nintendo DS is an absolute gem of a game in my opinion.
https://i.ytimg.com/vi/wRtNl6JQcj8/maxresdefault.jpg

It's a metroidvania type of game, but with some Megaman influences, and even a sort of strange pet-sim aspect to it too. You play as a girl who gets lost in a monster world, and you end up finding this baby monster that you raise and evolve through the game in different ways as you fight off the bosses and save the monster world from the control of the main villain.
It's a ton of fun, has challenge, and is honestly just one of my favorite games in general. It's so little known about that I barely find things of it on YouTube, but I did hear once they were supposed to have a 3DS remake which got pushed over to the Switch, but I dunno how legit that is, sadly.