Lagonna-Band Trailblazer

Heroic — Whenever you cast a spell that targets Lagonna-Band Trailblazer, put a +1/+1 counter on Lagonna-Band Trailblazer.

Conclave Mentor

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on that creature instead.
When Conclave Mentor dies, you gain life equal to its power.

Blossoming Sands

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {G} or {W}.

Chronicler of Heroes

When Chronicler of Heroes enters, draw a card if you control a creature with a +1/+1 counter on it.

Pheres-Band Warchief

Vigilance, trample
Other Centaur creatures you control get +1/+1 and have vigilance and trample.

Centaur Battlemaster

Heroic — Whenever you cast a spell that targets Centaur Battlemaster, put three +1/+1 counters on Centaur Battlemaster.

Hydra's Growth

Enchant creature
When Hydra's Growth enters, put a +1/+1 counter on enchanted creature.
At the beginning of your upkeep, double the number of +1/+1 counters on enchanted creature.

Reap What Is Sown

Put a +1/+1 counter on each of up to three target creatures.

Centaur's Herald

{2}{G}, Sacrifice Centaur's Herald: Create a 3/3 green Centaur creature token.

Plains

Gaea's Gift

Put a +1/+1 counter on target creature you control. It gains reach, trample, hexproof, and indestructible until end of turn. (It can't be the target of spells or abilities your opponents control. Damage and effects that say "destroy" don't destroy it.)