Undead Hexspeaker

Parley — Whenever Undead Hexspeaker attacks,
each player reveals the top card of their library.
For each nonland card revealed this way, create a Treasure token. Then each player draws a card.
Whenever players reveal the top card of their libraries for a parley ability, until your next turn,
your opponents can't cast spells with mana value
X or greater, where X is the lowest mana value
among nonland cards revealed this way.