The ancient civilization of the holy Vayar Mountains is no more, but their legacy can be found in the strangest places. Such as in an icy cave on a secluded each... That is where the terrible Forgotten Vayar has awakened.
When the Forgotten Vayar says "The caverns call to me!" you need to climb onto the boss as he will be jumping away.
If the Forgotten Vayar says anything else while doing a similar animation, he will be doing a belly flop move that will stun you and him when he lands, so you should climb onto his back then too.
If he doesn't say anything while charging the move, it's a fakeout and he will stun you if you are on his back.