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My original idea was a straight up cockatrice but that's kinda boring, so I merged it with a cockatoo/tiel
Coqui ("cocky", slang name for cockatoo + coquille, french for "shell") would evolve by levelling up with a frog Pokemon like Croagunk - in mythology a Cockatrice hatches from a chicken's egg incubated by a toad.
Normal/Flying -> Normal/Dragon
HP: 60
Atk: 50
Def: 54
Sp. Atk: 85
Sp. Def: 54
Speed: 116
BST: 419 (similar to regional rodents)
Abilities: Competitive/Early Bird
HA: Adaptability
Basically it would be a chance to use a dragon early in the game, that with its hidden ability, could be surprisingly strong in lower tiers.
Early game movepool would include things like Echoed Voice, Glare, Dragon Breath, Snarl and Uproar; eventually getting Boomburst, Hyper Voice and Flamethrower, too.