Why does crystal metagross exist?

I don’t see a point to it, its type means really nothing, it could’ve just been a pure grass type. It has one new move which is a slightly better mach punch, and to top it all off, its BST is worse than regular mega delta ruin metagross (try saying that 5 times fast)
Is there like a real lore reason? I haven’t picked that up
Just curious, i guess a mega evolution having a unique type with no weaknessess it neat, but in execution it’s just, a mono grass type with extra flair

I did some digging and I discovered its a crossover with a fangame ive never heard of that looks really cool, i feel mean now. Sorry. I didn’t know

What’s it called?

Pokemon Azurite, here’s their website: https://www.projectazurite.com/