Powerbalance (Modern Horizons 3 #495)

Powerbalance {R}{R}

Enchantment

Whenever an opponent casts a spell, you may reveal the top card of your library. If you do, you may cast that card without paying its mana cost if the two spells have the same mana value.

Illustrated by Liiga Smilshkalne

Standard
Alchemy
Pioneer
Explorer
Modern
Historic
Legacy
Brawl
Vintage
Timeless
Commander
Pauper
Oathbreaker
Penny