Shadowfax, Lord of Horses

Swing, and something smaller than a 4/4 comes off the top of your hand into the red zone already tapped and attacking: a Sneak Attack effect narrowed by a power gate rather than an exile clause. That trigger is where the design lives, and it reads as top-down flavor that happens to build a coherent tempo engine. The haste grant to your Horses is the setup line; the deployment is the payoff, and the two share a color pair because the cheat-into-combat instinct is Gruul-adjacent aggression wearing white's tribal-support coat. What keeps the trigger from spiraling is the "lesser power" restriction: everything it deploys has to come in strictly under the 4/4, so you are curving a rider into combat rather than dropping a haymaker, and each attack adds one body, not a board. Note the seam the rules leave here: a creature put in attacking this way was never declared as an attacker, so its own "whenever this attacks" text stays quiet; what you buy is a free body in the combat math, not a chain of attack triggers. That reframes the ideal target toward enters-the-battlefield payoffs and raw evasive damage rather than combat-declaration engines. The flavor sits underneath cleanly: the fastest horse in Middle-earth grants speed to the herd and outpaces whatever waits behind. As tribal design it is unusual in leading with a combat-cheat instead of an anthem, giving the Horse type an aggressive engine rather than another lord that only counts creatures already on the table.