Yig

Deathtouch, Double Strike, Indestructible, Hexproof.
At the beginning of your upkeep, flip a coin. If it lands on tails, flip that coin again until it lands on heads. place X X/X snake creature tokens with trample onto the battlefield, where X is how many times the coin landed on tails.
Target opponent has their library face up and their casted permanents enter the battlefield tapped until Yig leaves the battlefield.