Might of the Masses

Target creature gets +1/+1 until end of turn for each creature you control.

Tangle

Prevent all combat damage that would be dealt this turn.
Each attacking creature doesn't untap during its controller's next untap step.

Elvish Mystic

Timberwatch Elf

{T}: Target creature gets +X/+X until end of turn, where X is the number of Elves on the battlefield.

Forest

Wellwisher

{T}: You gain 1 life for each Elf on the battlefield.

Llanowar Elves

Elvish Vanguard

Whenever another Elf enters, put a +1/+1 counter on Elvish Vanguard.

Fyndhorn Elves

Lys Alana Huntmaster

Whenever you cast an Elf spell, you may create a 1/1 green Elf Warrior creature token.

Aspect of Hydra

Target creature gets +X/+X until end of turn, where X is your devotion to green. (Each {G} in the mana costs of permanents you control counts toward your devotion to green.)

Wirewood Pride

Target creature gets +X/+X until end of turn, where X is the number of Elves on the battlefield.