Dionus, Elvish Archdruid

Elves you control have "Whenever this creature becomes tapped during your turn, untap it and put a +1/+1 counter on it. This ability triggers only once each turn."

Boss's Chauffeur

This creature enters with a number of +1/+1 counters on it equal to one plus the number of other creatures you control.
Alliance — Whenever another creature you control enters, put a +1/+1 counter on this creature.
When this creature dies, create a 1/1 green and white Citizen creature token for each +1/+1 counter on it.

Aragorn and Arwen, Wed

Vigilance
Whenever Aragorn and Arwen enters or attacks, put a +1/+1 counter on each other creature you control. You gain 1 life for each other creature you control.

Cloakwood Swarmkeeper

Gathered Swarm — Whenever one or more tokens you control enter, put a +1/+1 counter on this creature.

Armorcraft Judge

When this creature enters, draw a card for each creature you control with a +1/+1 counter on it.

Arwen, Weaver of Hope

Each other creature you control enters with a number of additional +1/+1 counters on it equal to Arwen's toughness.

Celebrity Fencer

Alliance — Whenever another creature you control enters, put a +1/+1 counter on this creature.

Arwen, Mortal Queen

Arwen enters with an indestructible counter on it.
{1}, Remove an indestructible counter from Arwen: Another target creature gains indestructible until end of turn. Put a +1/+1 counter and a lifelink counter on that creature and a +1/+1 counter and a lifelink counter on Arwen.

Allosaurus Shepherd

This spell can't be countered.
Green spells you control can't be countered.
{4}{G}{G}: Until end of turn, each Elf creature you control has base power and toughness 5/5 and becomes a Dinosaur in addition to its other creature types.

Devoted Druid

{T}: Add {G}.
Put a -1/-1 counter on this creature: Untap this creature.

Ajani's Comrade

Trample
At the beginning of combat on your turn, if you control an Ajani planeswalker, put a +1/+1 counter on this creature.

Atomwheel Acrobats

Whenever you roll a 1 or 2, put that many +1/+1 counters on this creature.
{2}{G}: Roll a six-sided die.

Black Panther, Wakandan King

First strike
Survey the Realm — Whenever Black Panther or another creature you control enters, put a +1/+1 counter on target land you control.
Mine Vibranium — {3}: Move all +1/+1 counters from target land you control onto target creature. If one or more +1/+1 counters are moved this way, you gain that much life and draw a card.

Decorated Champion

Whenever another Warrior your team controls enters, put a +1/+1 counter on this creature.

Bramblewood Paragon

Each other Warrior creature you control enters with an additional +1/+1 counter on it.
Each creature you control with a +1/+1 counter on it has trample.

Chance-Met Elves

Whenever you scry, put a +1/+1 counter on this creature. This ability triggers only once each turn.