Beautiful design. The feel reminds me of my childhood, some of the best 2d platformers came out mid/end of 90’s right around the 3d hype. Rayman, Yoshi’s Island...

Yes, that's right. Yoshi's Island, for example, is a great inspiration for me.

That looks great. Some of the outdoor backgrounds remind me of Rastan.

I didn't know Rastan at all. It's kind of crazy, you always think you know all the games from that time and yet you stumble across one every now and then where you think, that would have been my thing back then :)

looks fantastic and now on my wishlist. As just starting out developing a game myself, what engine are you using?

The engine I'm using is based on this one with lots of customizations:

https://github.com/blitz-research/monkey

Looks beautiful