Althyr, Stormbound Wyrm

Flying, indestructible
If Althyr would enter, if it wasn't cast or no mana
was spent to cast it, exile it instead.
Whenever you cast a blue instant spell, exile
that card instead of putting it into your graveyard
as it resolves. If you do, it becomes plotted. Create
a 2/2 blue Drake creature token with flying.