Commune with Syllos

{u}{u}, Sacrifice a creature: Put an offering counter on Commune with Syllos. You may only use this ability once per turn.
At the beginning of your upkeep, if there are 3 or more offering counters on Commune with Syllos, sacrifice it, shuffle all creatures into their owners' decks , and summon a 9/9 blue unblockable Dragon creature token named "Syllos, Monster of the Deep."