What is the hardest Boss in a Sonic Game?

The Death Egg Robot from Sonic the Hedgehog 2

I remember...

Sonic's 2 Final Boss, how painful
Egg সর্প from Sonic Adventure haha
Eggman in Labrinth Zone from the original Sonic 1, how can I forget that

The final boss in Sonic the hedgehog 2. Literally, 16 hits to destroy this motherfucker.