Winged Hive Tyrant

Flying, haste
The Will of the Hive Mind — Other creatures you control with counters on them have flying and haste.

Tainted Strike

Target creature gets +1/+0 and gains infect until end of turn. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Sadistic Hypnotist

Sacrifice a creature: Target player discards two cards. Activate only as a sorcery.

Nath of the Gilt-Leaf

At the beginning of your upkeep, you may have target opponent discard a card at random.
Whenever an opponent discards a card, you may create a 1/1 green Elf Warrior creature token.

Genestealer Patriarch

Genestealer's Kiss — Whenever Genestealer Patriarch attacks, put an infection counter on target creature defending player controls.
Children of the Cult — Whenever a creature with an infection counter on it dies, you create a token that's a copy of that creature, except it's a Tyranid in addition to its other types.

Clamavus

Proclamator Hailer — Each creature you control gets +1/+1 for each +1/+1 counter on it.

Knight Exemplar

First strike (This creature deals combat damage before creatures without first strike.)
Other Knight creatures you control get +1/+1 and have indestructible. (Damage and effects that say "destroy" don't destroy them.)

Markov's Servant

Chosen of Markov

{T}, Tap an untapped Vampire you control: Transform Chosen of Markov.

Chosen of Markov // Markov's Servant

Genestealer Locus

Neurotraumal Rod — Whenever a creature attacks you, it gets -1/-0 until end of turn.
Whenever a creature attacks one of your opponents, it gets +0/+1 until end of turn.

Wing Shredder

Reach
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Getting

Bird Admirer

Reach
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Bird Admirer // Wing Shredder

Breathkeeper Seraph

Flying, soulbond (You may pair this creature with another unpaired creature when either enters. They remain paired for as long as you control both of them.)
As long as Breathkeeper Seraph is paired with another creature, each of those creatures has "When this creature dies, you may return it to the battlefield under its owner's control at the beginning of your next upkeep."

Ultramarines Honour Guard

Squad {2} (As an additional cost to cast this spell, you may pay {2} any number of times. When this creature enters, create that many tokens that are copies of it.)
Other creatures you control get +1/+1.

Crusader of Odric

Crusader of Odric's power and toughness are each equal to the number of creatures you control.

Defiant Bloodlord

Flying
Whenever you gain life, target opponent loses that much life.

Master of Dark Rites

{T}, Sacrifice another creature: Add {B}{B}{B}. Spend this mana only to cast Vampire, Cleric, and/or Demon spells.

Fiendslayer Paladin

First strike (This creature deals combat damage before creatures without first strike.)
Lifelink (Damage dealt by this creature also causes you to gain that much life.)
Fiendslayer Paladin can't be the target of black or red spells your opponents control.

Space Marine Devastator

Squad {2} (As an additional cost to cast this spell, you may pay {2} any number of times. When this creature enters, create that many tokens that are copies of it.)
Grav-cannon — When Space Marine Devastator enters, destroy up to one target artifact or enchantment.

Geth, Lord of the Vault

Intimidate (This creature can't be blocked except by artifact creatures and/or creatures that share a color with it.)
{X}{B}: Put target artifact or creature card with mana value X from an opponent's graveyard onto the battlefield under your control tapped. Then that player mills X cards.