Concordant Crossroads

Craterhoof Behemoth

Haste
When Craterhoof Behemoth enters, creatures you control gain trample and get +X/+X until end of turn, where X is the number of creatures you control.

Heedless One

Trample
Heedless One's power and toughness are each equal to the number of Elves on the battlefield.

Sylvan Messenger

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
When Sylvan Messenger enters, reveal the top four cards of your library. Put all Elf cards revealed this way into your hand and the rest on the bottom of your library in any order.

Ezuri, Renegade Leader

{G}: Regenerate another target Elf.
{2}{G}{G}{G}: Elf creatures you control get +3/+3 and gain trample until end of turn.

Llanowar Elves

Seeker of Skybreak

Priest of Titania

{T}: Add {G} for each Elf on the battlefield.

Doubling Chant

For each creature you control, you may search your library for a creature card with the same name as that creature. Put those cards onto the battlefield, then shuffle.

Reclamation Sage

When Reclamation Sage enters, you may destroy target artifact or enchantment.

Forest

Glimpse of Nature

Whenever you cast a creature spell this turn, draw a card.

Elvish Archdruid

Other Elf creatures you control get +1/+1.
{T}: Add {G} for each Elf you control.

Fyndhorn Elves

Quirion Ranger

Return a Forest you control to its owner's hand: Untap target creature. Activate only once each turn.