discarding half-breed/super munchkin

[kbra16]

Can you discard half-breed or super munchkin or any of its counterparts at anytime? I know that you can discard classes or races at any time.

But for example, a monster is on top, and the next player is a cleric. Needing to discard a card to put something on top, but say I have thief, I need that to possibly backstab. So can I discard just super munchkin? The rules explicitly say that you cannot discard "items" just because you want to, but this is not an item. If I had another class, say warrior, I could discard warrior and super munchkin and be just fine, but if I only have one class and super munchkin?