"The regal, artistic elf is one of the oldest living races. Perhaps their ability to live peacefully with their environment is one of the reasons they have survived while other races have died out."Summon Elf is a second-level Nature Magic spell in Heroes of Might and Magic IV that costs three spell points and summons a number of Elves based on the level of the caster.
As with most level 2 and 3 summoning spells, the number of elves you can summon with this spell probably isn't enough to really affect the battle. If you have enemy walkers tied down with quicksand, you might want to summon a few groups of elves to increase your ranged offensive capability.
Remember to wait until you have summoned a large number of elves before shooting any arrows, as summoning more creatures doesn't increase the available ammo, and shooting with the small number of elves you start with might just be wasting arrows.