Mystical Teachings is a common Instant card from Time Spiral (TSP), collector number 69. Current market price: $0.31 (foil $15.97), TCGplayer market prices via Scryfall.
Search your library for an instant card or a card with flash, reveal it, put it into your hand, then shuffle. Flashback {5}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)