Floating Island 4
Well, Sharpknux has issued yet another version, and as usual the "giant squid" got me when I went under the raft, and from the raft I still couldn't bounce all the way up inside - though I reached the tunnel level, where I gained much ammo before doing something wrong and finding myself respawned in the sky-drop tunnel, sigh...
For a change, the screenshot is taken while I was in "ghost" mode, which allows us to see the devious inner workings of the island! One thing this shot does not show is the hidden complex of rather large rooms, reached by diving right into one of the corners of the ocean below. This might make a perfectly decent map on its own - though of course, as a place to fight it has the major drawback that, after a battle, the defeated player respawns back in the main part of the map, far far away! Still, you have to give our friendly mapmaker credit for sneaking in a whole lot of added exploration value!