When I was running my Queston campaign in the late 80's for my high school friends and college buddies, I used parts of DUNGEONLAND to fill out the mythical continent of (this is a mouthful) Mythophantarealean (!)
I used the Smilodon Cat, the Mad Hatter and the Caterpillar atop the mushroom to great effect.
I have no experience with BEYOND THE MAGIC MIRROR, but it looks like it comes from a similar vein and could be of great use in any madhouse dungeon.
Gary Gygax must have used these (or similar) in Castle Greyhawk. Here's part of the introduction from MAGIC MIRROR:
I don't know if he ever reference these modules in Castle Greyhawk (or elsewhere).
ENTERING THE LAND BEYOND THE MAGIC MIRRORThe entry point for The Land Beyond the Magic Mirror will beshown on the proper level of the Greyhawk Castle Dungeonseries when it is finally done. As that is likely to be years fromnow, it is probable that you will be inserting this module intoyour existing campaign.
DOWNLOAD BOTH MODULES HERE BEFORE THEY ARE GONE!