Wasn't there a thread like this not so long ago?
Anyway I believe I answered it was the Thunder Bird from Zelda 2. Harder than Dark Link for sure, I only died a handful of times against him (without cheating even). I remember beforehand, my number of Game Overs getting to that point was in the 60s. Afterwards, it was over 120. And you have 3 lives in that game, so 60 extra Game Overs means 180 deaths!







