So X is Ground, Y is Flying, and Z is Flying? --- I'm not easily impressed; I'm usually oblivious to whatever's in front of me. Stunfisk is the epitome of monstrous majestic legendary creatures that spew fire.
In Norse mythology, at the top of Yggdrasil tree is an eagle, on the ground are four stags, and along its roots slithers a serpent-like dragon. It's underground and resides in the Realm of the Dead or something so Ghost would fit in with that theme too.
I hope it's at least Poison though, that type needs a legendary.