Forest

Growth-Chamber Guardian

{2}{G}: Adapt 2. (If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.)
Whenever one or more +1/+1 counters are put on Growth-Chamber Guardian, you may search your library for a card named Growth-Chamber Guardian, reveal it, put it into your hand, then shuffle.

Imperious Perfect

Other Elves you control get +1/+1.
{G}, {T}: Create a 1/1 green Elf Warrior creature token.

Wildborn Preserver

Flash (You may cast this spell any time you could cast an instant.)
Reach (This creature can block creatures with flying.)
Whenever another non-Human creature you control enters, you may pay {X}. When you do, put X +1/+1 counters on this creature.

Marwyn, the Nurturer

Whenever another Elf you control enters, put a +1/+1 counter on Marwyn, the Nurturer.
{T}: Add an amount of {G} equal to Marwyn's power.

Llanowar Elves

Elvish Champion

Other Elf creatures get +1/+1 and have forestwalk. (They can't be blocked as long as defending player controls a Forest.)

Yavimaya, Cradle of Growth

Each land is a Forest in addition to its other land types.

Elvish Harbinger

When Elvish Harbinger enters, you may search your library for an Elf card, reveal it, then shuffle and put that card on top.
{T}: Add one mana of any color.

Pelt Collector

Whenever another creature you control enters or dies, if that creature's power is greater than Pelt Collector's, put a +1/+1 counter on Pelt Collector.
As long as Pelt Collector has three or more +1/+1 counters on it, it has trample.

Llanowar Visionary

When Llanowar Visionary enters, draw a card.
{T}: Add {G}.

Elvish Archdruid

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