Counterflux is a rare Instant card from Secret Lair Drop (SLD), collector number 482. Current market price: $2.64 (foil $2.51), TCGplayer market prices via Scryfall.
This spell can't be countered. Counter target spell you don't control. Overload {1}{U}{U}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")