Zyrixal, Herald of the Abyss

Whenever a player sacrifices one or more creatures, each player mills three cards. put a land milled this way onto
the battlefield under your control tapped.

At the beginning of each upkeep, create a 1/1 green Tentacle creature token.

{5}{u}{b}{g}, Sacrifice three Tentacles: Create a 10/10 black
and green Kraken Horror creature token with trample and
“Whenever this creature deals combat damage to a player, that player mills half their library, rounded up.”