I could easily see this becoming really popular! I love games like this where you can raise and collect (and, in this case, merge) little creatures.
I also LOVE this dark fantasy pixel art style you decided to use. While a lot of those kinda games are more cutesy and inspired by Pokémon / Tamagotchi, this game is more unique with it's art style and also a more grim story.
It's giving a mix of Darkest Dungeon and the lesser known Monster Girl Manager.
I agree with yonodusk that it would make for a fun mobile game. Idle games are also a "guilty pleasure" of mine, not just on mobile but just also in another window on my Laptop while I'm doing something else, so I'd say I'm in the target audience for stuff like this :D
All in all, I see potential. The game would need more polish, though. Just like yonodusk I also couldn't figure out the spells and sometimes the fights get stuck in endless loops. I'd look forward to play this more once it has more content though!