I am going to tell you right now, you have to click on this image and bring it up to full size to appreciate it. There is so much detail put into this! This is, of course, the boss battle against Phantom Ganon from Ocarina of Time. Definitely an action packed battle, this villain keeps you on your toes at all times.
This work of art was created by Txikimorin on deviantart. I love the depiction of Ganon! He looks like something out of a deep, hellish abyss. It is just an overload of awesome detail that should be viewed in full size. If you like this art, Txikimorin has drawn some other Zelda boss fights on his deviantart account here.