Champion of Stray Souls is a mythic Creature — Skeleton Warrior card from Commander 2015 (C15), collector number 119. Current market price: $0.34, TCGplayer market prices via Scryfall.
{3}{B}{B}, {T}, Sacrifice X other creatures: Return X target creature cards from your graveyard to the battlefield. {5}{B}{B}: Put this card from your graveyard on top of your library.