EvoWorld.io

EvoWorld.io (originally released as Fly or Die) starts you as one of the food chain's smallest links, a fly, and ties every evolution to actually surviving long enough to eat, which means the early minutes spent as a weak, vulnerable creature matter just as much as the powerful late-game forms.

Each creature swap changes your abilities entirely rather than just your stats, so a strategy built around a previous form's strengths often stops working the moment you evolve into something with a different diet or movement style. Staying near the edges of an ecosystem rather than its busiest hunting grounds tends to keep smaller, less-evolved players alive long enough to reach a form that can actually compete. Fish Eat Fish runs a similar grow-by-eating food chain entirely underwater.