Barrensteppe Siege is a rare Enchantment card from Tarkir: Dragonstorm Promos (PTDM), collector number 171p. Current market price: $0.37 (foil $0.36), TCGplayer market prices via Scryfall.
As this enchantment enters, choose Abzan or Mardu. • Abzan — At the beginning of your end step, put a +1/+1 counter on each creature you control. • Mardu — At the beginning of your end step, if a creature died under your control this turn, each opponent sacrifices a creature of their choice.