Ipnu Rivulet is a uncommon Land — Desert card from Hour of Devastation (HOU), collector number 180. Current market price: $0.24 (foil $3.90), TCGplayer market prices via Scryfall.
{T}: Add {C}. {T}, Pay 1 life: Add {U}. {1}{U}, {T}, Sacrifice a Desert: Target player mills four cards. (They put the top four cards of their library into their graveyard.)