There is a rare Bug where the Firebird is slowly but surly going down to the Ground until he is trying to pushing the ground to going under the map (Thankfully, it doesn’t work) and Start to Skate the soil like Skateboarding. Unable to Attack!
I encountered this briefly as well.
I then proceeded to jump on it and it eventually took off again! Unfortunately I only got a short way before I fell off it, but it was really cool!