Prophecy Forseen

(You may cast a legendary instant only if you control
a legendary creature or planeswalker.)
This spell costs {4} less to cast if an opponent has
their commander on the battlefield.
Scry X, where X is the number of legendary permanents on the battlefield, then draw 3 cards.
For the rest of the game, legendary spells you
cast can't be countered unless any opponent
pays {2}.