No monster, but my 9in Jack Dempsey after he fights the net for a 10 mins and he gives up and I pull him out right when he hits the surface of the water... Its starts to rain. My yoyo loaches are a PITA so fast!
Foot long fire eel, I swear it moved quicker UNDER the sand than through the water!! Ended up getting almost everything else out of the tank, including the water!
I have a zodiac loach that i've had to move a few times. Always a huge ordeal, sometimes it will take days of random net attacks to finally get him, or i'll end up kicking a bunch of sand into my filter... always something with him.