Somewhere in the ancient, not!Aztec jungle death temple, you enter a room which closes behind you. In the center of the room is the BLOOD POOL. Every round, 1d6 zombies shuffle out of the blood pool. They walk slowly towards opening GOLDEN MOUTHS. Every zombie has an elemental affinity; the scorched ones are related to fire, the chilled blue ones related to ice, and the glowing phosphorescent ones are related to lightning.
If one of the zombies reaches a golden mouth and is devoured, the ancient idol in the center of the room belches a powerful elemental spell. For a fire zombie that is eaten, it's a fireball. If it's a lightning zombie- chain lightning. If it's ice? The floor freezes and you take 1d6 ice damage a turn or something like that. The idol casts spells at least as a name level sorcerer, if not worse. Essentially, it's not survivable to let zombies into the mouths.
The zombies are slow and don't really fight back unless if you try to block them from moving towards the golden mouth. You can strike them without a to-hit roll; you just deal damage. If you kill a zombie next to zombie of a matching element, the nearby zombies will take 1d6 damage in a little explosion. Using this, you can chain together zombie kills to clear the waves of zombies quickly before you are overrun. Once you've slain enough zombies, or enough rounds have passed, the giant idol is forced to power down and let you pass.