Use undead, use more monsters, spread the monsters out so sleep won't get many of them, use one or two monsters that have enough HD to be immune instead of many weak monsters, have monsters launch their attacks from out of sleep range (missiles, boulders rolled down hills, etc.), create wimpy versions of automatons to use on low level characters (the living statues and golems from B/X can provide good inspiration for these).
Also use more traps! Sleep doesn't help with those.
Last edited by Blackadder23 (1/12/2015 1:39 pm)