Besides the huge amount of source material for inspiration, open to so many intepretations, I love how it doesn't restrict mechanics at all. I have more ideas for that theme that any other before:

• A pet simulator where you need to take care of a Griffin or Cerberus.

• A Pac-Man style game where you play as the Wendigo from American Indian folklore, chasing down people to eat them.

• A stealth game where you need to avoid a Minotaur as you escape the Labyrinth.

• An idea I had for "Mirror" was a game where you're hunting Medusa, but you can't look directly at her, only her reflection around corners.

• A racing game like Mario Kart on Rainbow Road, where you're chasing a Leprechaun to the end of the rainbow to steal his pot of gold.

• A Pokémon Snap style game where you're trying to snap pictures of Bigfoot or the Loch Ness Monster.

• A quiz game featuring the Sphix.

• A sea battle simlulator where you need to fight off a Kraken.

• A simulator where you're a Mermaid having to do Seaworld-style tricks.

• The Monkey King of Chinese folklore could have mechanics based of either the cloud he rides on, or his shrinking/extending staff.

• A hunting simulator where you need to track and kill a Jackalope.

• A sumo game where you play as Paul Bunyan competing against Goliath.

Those are just what I came up with in about 5 minutes.