Upgrade your heart potions to the max that way they restore all hearts and can be used twice. Also, take the Horde little by little, dont just run into the fight. Especially with the giant Bokoblins with the Shields (forgot the name haha). Lure one away from the others and slaughter. For the Archers, shoot them from afar, using their own arrows (once the hit the ground) to replenish yours.
I beat it with two maxed out heart potions and two fairies and ended up only using one fairy this way (to replenish my hearts to the max) and still had the potions for Ghirahim (I do the Horde/Boss Rush for fun in Hero mode all the time). Good luck!