It’s most likely Agar.io. In that game, you control a blob that grows by eating smaller blobs and avoiding bigger ones.

Why that matches

  • The core loop is exactly “eat smaller blobs, get bigger.”
  • It became the iconic game for that mechanic and is often what people mean when they describe a “blob eats smaller blobs” game.

Close alternatives

  • Blob.io and similar .io games use the same basic idea, but they’re newer clones or variations.
  • Tales From Space: About a Blob is a different, more platform-style game and is less likely if you mean the online blob-eat-blob game.

If you want, I can also name a few similar games with the same mechanic.