Chord of Calling is a rare Instant card from Secret Lair Drop (SLD), collector number 1595. Current market price: $29.80, TCGplayer market prices via Scryfall.
Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.) Search your library for a creature card with mana value X or less, put it onto the battlefield, then shuffle.