This is a Bant counters deck that splashes white for extra synergy, protection and midrange versatility.
In the mainboard:
Llanowar Elves
and
Incubation Druid
provides ramp.
Biomancer's Familiar
reduces the cost of Adapt and other activated abilities.
Hydroid Krasis
provides card advantage, life gain, and a late game swinger.
Growth-Chamber Guardian
helps build your board early.
Shapers of Nature
provides extra card draw and counters and is enabled by
Biomancer's Familiar
.
Shalai, Voice of Plenty
protects you and your other creatures, while also providing a way to increase the +1/+1 counters on all of your creatures, which also synergizes with
Biomancer's Familiar
.
Herald of Secret Streams
provides a win condition and a way to push your creatures through blockers for matchups against decks with lots of creatures or blockers.
Knight of Autumn
provides a versatile option that can provide +1/+1 counters, life gain, or removal for artifacts and enchantments in matchups where that is relevant.
Zegana, Utopian Speaker
provides some card draw, gives trample, and a potentially large creature.
Ajani, Adversary of Tyrants
provides further +1/+1 counters and a means to reanimate your cheap creatures from the graveyard in the face of removal or if they die in combat.
Vivien Reid
provides card advantage, removal, and an ultimate which significantly boosts and protects your creatures and puts them over the top to gaurantee victory.
Stony Strength
and
Assure / Assemble
provides further +1/+1 counters and some protection from removal.
Conclave Tribunal
provides removal in a way that synergizes with the rest of the deck.
Incubation / Incongruity
provides a little card advantage and removal for large threats.
In the sideboard:
Dive Down
and
Sheltering Light
helps provide protection against removal.
Unbreakable Formation
protects your creatures against mass removal while also providing +1/+1 counters and another way to push your creatures through combat.
Deputy of Detention
and
Ixalan's Binding
provides further removal.
Settle the Wreckage
provides mass removal and defense against aggro.
