Flying Snake

It has one requirement and it is not a progression gate. Stand in front of bare Lihzahrd Brick Wall and they start coming, along with Lihzahrds. The wall at the temple entrance counts, so a curious player who wanders over for a look long before hardmode gets jumped by the hardest hitting enemy available at that stage of the game. Nothing summons them and nothing else triggers them.

The attack is simple: a straight line at you and contact damage, the same approach a bat takes, with nothing else in the kit. Knockback keeps them off. Inside the temple the corridors are the real problem, since snakes round corners at head height while lizards close along the floor. Clear the vertical space before you push forward, and do not let yourself get pinned in a two tile gap.

The design points at Quetzalcoatl, the feathered serpent of Mesoamerican myth, and possibly at the real gliding snakes of Southeast Asia.