Aethermancer's Decree

At the beginning of each player's upkeep, if that
player has more than X cards in their hand, they
must discard cards until they have X cards in
hand. Whenever a permanent enters the
battlefield under an opponent's control, if that permanent's converted mana cost is equal to or greater than the number of cards in their hand, counter that spell.
"In the realm of unraveled plans, the overreaching
mage meets their undoing. Every conjuration, a step towards their own collapse."