Aven Courier

Flying
Whenever this creature attacks, choose a counter on a permanent you control. Put a counter of that kind on target permanent you control if it doesn't have a counter of that kind on it.

Devoted Druid

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

Aven Mimeomancer

Flying
At the beginning of your upkeep, you may put a feather counter on target creature. If you do, that creature has base power and toughness 3/1 and has flying for as long as it has a feather counter on it.

Wall of Roots

Defender
Put a -0/-1 counter on this creature: Add {G}. Activate only once each turn.

Incubation Druid

{T}: Add one mana of any type that a land you control could produce. If this creature has a +1/+1 counter on it, add three mana of that type instead.
{3}{G}{G}: Adapt 3. (If this creature has no +1/+1 counters on it, put three +1/+1 counters on it.)

Steelbane Hydra

This creature enters with X +1/+1 counters on it.
{2}{G}, Remove a +1/+1 counter from this creature: Destroy target artifact or enchantment.

Scavenging Ooze

{G}: Exile target card from a graveyard. If it was a creature card, put a +1/+1 counter on this creature and you gain 1 life.

Skyship Plunderer

Flying
Whenever this creature deals combat damage to a player, for each kind of counter on target permanent or player, give that permanent or player another counter of that kind.

Tidus, Yuna's Guardian

At the beginning of combat on your turn, you may move a counter from target creature you control onto a second target creature you control.
Cheer — Whenever one or more creatures you control with counters on them deal combat damage to a player, you may draw a card and proliferate. Do this only once each turn.

Perrie, the Pulverizer

When Perrie enters, put a shield counter on target creature. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
Whenever Perrie attacks, target creature you control gains trample and gets +X/+X until end of turn, where X is the number of different kinds of counters among permanents you control.

Thrummingbird

Flying
Whenever this creature deals combat damage to a player, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)