Mausoleum Secrets is a rare Instant card from Guilds of Ravnica (GRN), collector number 75. Current market price: $0.87 (foil $3.41), TCGplayer market prices via Scryfall.
Undergrowth — Search your library for a black card with mana value less than or equal to the number of creature cards in your graveyard, reveal it, put it into your hand, then shuffle.