Mausoleum Secrets is a rare Instant card from Guilds of Ravnica Promos (PGRN), collector number 75p. Current market price: $2.14 (foil $4.72), 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.