Sunstrike Legionnaire

Sunstrike Legionnaire doesn't untap during your untap step.
Whenever another creature enters, untap Sunstrike Legionnaire.
{T}: Tap target creature with mana value 3 or less.

Soul Warden

Whenever another creature enters, you gain 1 life.

Nature's Claim

Destroy target artifact or enchantment. Its controller gains 4 life.

Cultivate

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Scute Swarm

Landfall — Whenever a land you control enters, create a 1/1 green Insect creature token. If you control six or more lands, create a token that's a copy of Scute Swarm instead.

Plains

Evolving Wilds

{T}, Sacrifice Evolving Wilds: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Mountain

Life and Limb

All Forests and all Saprolings are 1/1 green Saproling creatures and Forest lands in addition to their other types. (They're affected by summoning sickness.)

Forest

Sporemound

Landfall — Whenever a land you control enters, create a 1/1 green Saproling creature token.

Impact Tremors

Whenever a creature you control enters, Impact Tremors deals 1 damage to each opponent.

Congregation at Dawn

Search your library for up to three creature cards, reveal them, then shuffle and put those cards on top in any order.

Heliod's Pilgrim

When Heliod's Pilgrim enters, you may search your library for an Aura card, reveal it, put it into your hand, then shuffle.

Presence of Gond

Enchant creature
Enchanted creature has "{T}: Create a 1/1 green Elf Warrior creature token."

Ogre Battledriver

Whenever another creature you control enters, that creature gets +2/+0 and gains haste until end of turn. (It can attack and {T} this turn.)

Midnight Guard

Whenever another creature enters, untap Midnight Guard.

Splinter Twin

Enchant creature
Enchanted creature has "{T}: Create a token that's a copy of this creature, except it has haste. Exile that token at the beginning of the next end step."

Llanowar Elves

Goldnight Commander

Whenever another creature you control enters, creatures you control get +1/+1 until end of turn.

Nature's Lore

Search your library for a Forest card, put that card onto the battlefield, then shuffle.