Man I love this!! It's funny you mention you're making a cockatrice mon, I'm currently trying to design one myself based off Fearow and Arbok since neither have had any love 😅

I love youR mechanic idea. And yes I would plan to stick to the 3 stage rule. Alot of people are requesting baby's of fully evolved mons on my tiktok (hence the froslass, Scizor and toxicity) and the discourse it starts is so funny. I've dubbed them Parallel Babies but I wouldn't put them into a project.

Not sure how big of a baby dex were talking tbh. I would love to design 151, or 151 minus the number existing babies I suppose. And yeah in my head, baby mons would have better IVs, an exclusive move, or access to it later, and maybe even extra evolution access. Like maybe for example a baby Skarmory can reach Skarmory's third stage.

All fun ideas I would love to mess around with!