Yavimaya, Cradle of Growth

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

Marwyn, the Nurturer

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

Llanowar Elves

Pelt Collector

Whenever another creature you control enters the battlefield 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.

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.

Elvish Mystic

Elvish Harbinger

When Elvish Harbinger enters the battlefield, 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.

Elvish Champion

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

Elvish Archdruid

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

Forest

Wildborn Preserver

Flash
Reach
Whenever another non-Human creature enters the battlefield under your control, you may pay {X}. When you do, put X +1/+1 counters on Wildborn Preserver.

Imperious Perfect

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