Yew Spirit

Howlgeist

Creature — Spirit Wolf (4/2)

Creatures with power less than Howlgeist's power can't block it.
Undying (When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)

Wildwood Geist

Creature — Spirit (3/3)

Wildwood Geist gets +2/+2 as long as it's your turn.

Druid's Familiar

Creature — Bear (2/2)

Soulbond (You may pair this creature with another unpaired creature when either enters the battlefield. They remain paired for as long as you control both of them.)
As long as Druid's Familiar is paired with another creature, each of those creatures gets +2/+2.

Wolfir Silverheart

Creature — Wolf Warrior (4/4)

Soulbond (You may pair this creature with another unpaired creature when either enters the battlefield. They remain paired for as long as you control both of them.)
As long as Wolfir Silverheart is paired with another creature, each of those creatures gets +4/+4.

Craterhoof Behemoth

Creature — Beast (5/5)

Haste
When Craterhoof Behemoth enters the battlefield, creatures you control gain trample and get +X/+X until end of turn, where X is the number of creatures you control.

Flowering Lumberknot

Creature — Treefolk (5/5)

Flowering Lumberknot can't attack or block unless it's paired with a creature with soulbond.

Geist Trappers

Creature — Human Warrior (3/5)

Soulbond (You may pair this creature with another unpaired creature when either enters the battlefield. They remain paired for as long as you control both of them.)
As long as Geist Trappers is paired with another creature, both creatures have reach.

Nettle Swine

Creature — Boar (4/3)

Pathbreaker Wurm

Creature — Wurm (6/4)

Soulbond (You may pair this creature with another unpaired creature when either enters the battlefield. They remain paired for as long as you control both of them.)
As long as Pathbreaker Wurm is paired with another creature, both creatures have trample.

Soul of the Harvest

Creature — Elemental (6/6)

Trample
Whenever another nontoken creature enters the battlefield under your control, you may draw a card.

Evernight Shade

Creature — Shade (1/1)

: Evernight Shade gets +1/+1 until end of turn.
Undying (When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)

Narstad Scrapper

Artifact Creature — Construct (3/3)

: Narstad Scrapper gets +1/+0 until end of turn.

Sigarda, Host of Herons

Legendary Creature — Angel (5/5)

Flying, hexproof
Spells and abilities your opponents control can't cause you to sacrifice permanents.

Goldnight Commander

Creature — Human Cleric Soldier (2/2)

Whenever another creature enters the battlefield under your control, creatures you control get +1/+1 until end of turn.

Midvast Protector

Creature — Human Wizard (2/3)

When Midvast Protector enters the battlefield, target creature you control gains protection from the color of your choice until end of turn.

Undead Executioner

Creature — Zombie (2/2)

When Undead Executioner dies, you may have target creature get -2/-2 until end of turn.

Zealous Conscripts

Creature — Human Warrior (3/3)

Haste
When Zealous Conscripts enters the battlefield, gain control of target permanent until end of turn. Untap that permanent. It gains haste until end of turn.

Archwing Dragon

Creature — Dragon (4/4)

Flying, haste
At the beginning of the end step, return Archwing Dragon to its owner's hand.

Demonlord of Ashmouth

Creature — Demon (5/4)

Flying
When Demonlord of Ashmouth enters the battlefield, exile it unless you sacrifice another creature.
Undying (When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)

Dread Slaver

Creature — Zombie Horror (3/5)

Whenever a creature dealt damage by Dread Slaver this turn dies, return it to the battlefield under your control. That creature is a black Zombie in addition to its other colors and types.