Few years back, I "caught" a Hellbender on a prince nymph on the Nantahala. Thought I had a heavy fish on that just didn't move much. Scared the crap out of me when he grabbed my line and started pulling himself up. He got to keep that fly.
Also caught a rainbow who had already had a hook, from a previous fisherman, lodged in his tongue. The hook of my #20 BWO went into the eye of the other hook so I landed a fish without actually hooking it anywhere on its body. He was probably happy when I sent him back without either hook.