I've set up a mob spawner with Extra Utility's "Cursed Earth" and it works beautifully. Simple 5x5 spawn area with MFR Grinder, it produces 85-90 Mob Essence per hour and a good supply of mob drops. (And enough Slimeballs to make resin and rubber for a lifetime.) Now the question - how can I turn it off? Light is out of question. I've tried sticky pistons with slabs in the ceiling, this should only leave half a block gap between ceiling and floor. Apparently this also counts already as no gap at all and the earth turns into dirt. What other ways could you think of? Magma Torch etc doesn't work, the mobs are still spawning. Which is actually awesome, since the spawner is in my base which has a torch as spawn prevention. Water maybe? Would be easy to build a system that floods the area. What other ways would you suggest?