Glad you enjoyed the game! Unfortunately though, we do not plan to ever make merch for the game as to not anger the creators our game is based off of. Even if we may legally be allowed to. However, this may not stop others from making their own merch of the game, which we're fine with. You can however support the staff team as individual creators as we do produce other content you can pay for, or have kofi's in our bios (one example is twitter). But that's completely optional and no one should really be giving us money. XD
So long as the content is something you've drawn yourself, then yes you're free to make your own merch.
Quote from Nifast the Lead Artist : "as long as what's being sold are not actual official assets or material then yes".
If you do end up making merch send me a photo cause I'd love to see it lmao. Have fun.