Either Molgera or Puppet Ganon: Snake. But I guess I'd say Puppet Ganon. Kalle Demos comes in third, as you have to *constantly* move or get hit. No, I take that back. Ganondorf comes in third. Kalle Demos is fourth. (I guess the Helmeroc King would be fifth.)
I think the snake version of Puppet Ganon was the hardest, since timing is essential to beating him and it is something I am bad at, even though there were ways to slow him down.
lol, did you know that you can throw bait and he'll stop to eat it? XD
Haha, well all funny stuff aside, you can hit him in the head with your sword when he comes by, which will stun him long enough to get off a shot (if you're quick).