Scurry Oak

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
Whenever one or more +1/+1 counters are put on this creature, you may create a 1/1 green Squirrel creature token.

Soul Warden

Whenever another creature enters, you gain 1 life.

Herd Baloth

Whenever one or more +1/+1 counters are put on this creature, you may create a 4/4 green Beast creature token.

Triskelion

This creature enters with three +1/+1 counters on it.
Remove a +1/+1 counter from this creature: It deals 1 damage to any target.

Light of Promise

Enchant creature
Enchanted creature has "Whenever you gain life, put that many +1/+1 counters on this creature."

Cathars' Crusade

Whenever a creature you control enters, put a +1/+1 counter on each creature you control.

Soul's Attendant

Whenever another creature enters, you may gain 1 life.

Eladamri's Call

Search your library for a creature card, reveal that card, put it into your hand, then shuffle.

Walking Ballista

This creature enters with X +1/+1 counters on it.
{4}: Put a +1/+1 counter on this creature.
Remove a +1/+1 counter from this creature: It deals 1 damage to any target.

Sunbond

Spike Feeder

This creature enters with two +1/+1 counters on it.
{2}, Remove a +1/+1 counter from this creature: Put a +1/+1 counter on target creature.
Remove a +1/+1 counter from this creature: You gain 2 life.

Heliod, Sun-Crowned

Indestructible
As long as your devotion to white is less than five, Heliod isn't a creature.
Whenever you gain life, put a +1/+1 counter on target creature or enchantment you control.
{1}{W}: Another target creature gains lifelink until end of turn.

Rosie Cotton of South Lane

When Rosie Cotton enters, create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this token: You gain 3 life.")
Whenever you create a token, put a +1/+1 counter on target creature you control other than Rosie Cotton.

Lathiel, the Bounteous Dawn

Lifelink
At the beginning of each end step, if you gained life this turn, distribute up to that many +1/+1 counters among any number of other target creatures.

Luminous Phantom

Flying
Whenever another creature you control leaves the battlefield, you gain 1 life.
If Luminous Phantom would be put into a graveyard from anywhere, exile it instead.

Lunarch Veteran

Whenever another creature you control enters, you gain 1 life.
Disturb {1}{W} (You may cast this card from your graveyard transformed for its disturb cost.)

Lunarch Veteran // Luminous Phantom

Ivy Lane Denizen

Whenever another green creature you control enters, put a +1/+1 counter on target creature.