Wyverns are enemies in Solomon's Key.
Wyverns fly back and forth across a particular row of a stage. They don't particularly react to the player, but they will destroy any block that gets in their way before turning back around in the other direction. They turn around considerably slowly whenever they bumb into an indestructible wall. There is no wyvern in the NES version. The equivalent is the Devil Keese, which does not pause when it hits a wall.