Sheoldred, Whispering One is a mythic Legendary Creature — Phyrexian Praetor card from Magic Online Promos (PRM), collector number 40086.
Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.) At the beginning of your upkeep, return target creature card from your graveyard to the battlefield. At the beginning of each opponent's upkeep, that player sacrifices a creature of their choice.