D&D 5E [SPOILERS] Final encounter in Tyranny of Dragons and playing a wizard for 16 levels

[Fanaelialae]

You can do this with wish. If you do use wish to do it, you get to roll a 33% you never get to cast wish again.

An easier way to do it would be to have an ally fly over the dragon and then cast Polymorph on that ally to turn him into a whale. The fall might hurt your ally too but the "temp hp" from Polymorph should soak most (if not all) of the damage.