Uncanny Speed

The +3/+0 half is the lure, but the haste is what this is actually buying. As a pure pump spell, two mana for three power is unremarkable rate; what justifies the slot is the instant-speed window it opens on a creature that could not otherwise attack. Cast it on something just played and you turn a dead summoning-sick turn into lethal; cast it after blockers are declared and the +3/+0 settles a combat that was already going to happen. The haste rider is the part that creates a threat from nothing, and it is the part that makes the card a finisher rather than a trick. Red has a long line of these cheap haste-and-power instants designed to push a single creature over the line in one swing, and they live or die on whether the deck is built to convert that one big attacker into a closed game. Outside the all-in aggressive shell that wants exactly this effect, the floor is a worse Giant Growth that does not even hold up on defense; inside it, it is the burst that ends the race a turn early.