Legolas's Quick Reflexes

Split second on a one-mana green instant is the anomaly worth staring at, because green almost never gets it. The mechanic historically lived on cards built to jam an effect through a window opponents cannot touch: Sudden Shock, Krosan Grip. Grafting that window onto an untap-and-protect spell produces something green usually cannot buy at any price: an answer to instant-speed removal that itself cannot be answered. The core line is defensive. Untap a creature that has already attacked and it becomes an available blocker on your opponent's turn, a pseudo-vigilance effect green normally pays a keyword slot for; hand it hexproof and reach in the same beat and it dodges the removal and covers the air. What split second guarantees is that no one can cast a spell or activate a non-mana ability in response while the spell is on the stack: the untap, the hexproof, and the reach all land before anyone can interact, so committing a creature into open mana stops being a gamble. The tap-triggered burn clause is the odd one out and rewards careful reading. Because the buffs expire at end of turn, this is not a repeatable pinger; it fires only on taps that happen this turn. The obvious enabler is your own attack step: cast it on your turn, untap the creature, then swing, and the tap from attacking turns the buff into a Fight-style shot at another creature. It is a protective trick first and a damage source a distant second, and the split second is what makes the protection absolute rather than merely likely.