Larger snails, like fighting or queen conchs for example.
Also, there will eventually be things like annelid or polychaete (bristle) worms which will inevitably come out a night.
Zebra turbos are good ones for even aggressive tanks. They get big... like baseball/softball size and they are nocturnal which is when those hunters are sleeping.
I used to keep the bigger hermit crabs in my aggressive tank, but I'm not sure how much they actually cleaned, unless you count eating the scraps that the triggers would throw all over the tank. Maybe bulldozers like horseshoe crabs?
Nemo had some huge emerald crabs (like almost the size of a ping pong ball) - wonder if they'd put up a fight?