Kinzu of the Bleak Coven

Flying
Whenever another nontoken creature you control dies, you may pay 2 life and exile it. If you do, create a token that's a copy of that creature, except it's 1/1 and has toxic 1. (Players dealt combat damage by it also get a poison counter.)

Kalitas, Traitor of Ghet

Lifelink
If a nontoken creature an opponent controls would die, instead exile that card and create a 2/2 black Zombie creature token.
{2}{B}, Sacrifice another Vampire or Zombie: Put two +1/+1 counters on Kalitas, Traitor of Ghet.

Khenra Eternal

Afflict 1 (Whenever this creature becomes blocked, defending player loses 1 life.)

Killing Wave

For each creature, its controller sacrifices it unless they pay X life.

Kaya's Ghostform

Enchant creature or planeswalker you control
When enchanted permanent dies or is put into exile, return that card to the battlefield under your control.

Kalastria Nightwatch

Whenever you gain life, Kalastria Nightwatch gains flying until end of turn.

Knight of the Ebon Legion

{2}{B}: Knight of the Ebon Legion gets +3/+3 and gains deathtouch until end of turn.
At the beginning of your end step, if a player lost 4 or more life this turn, put a +1/+1 counter on Knight of the Ebon Legion. (Damage causes loss of life.)

Kalastria Healer

Rally — Whenever Kalastria Healer or another Ally you control enters, each opponent loses 1 life and you gain 1 life.

Kalitas, Bloodchief of Ghet

{B}{B}{B}, {T}: Destroy target creature. If that creature dies this way, create a black Vampire creature token. Its power is equal to that creature's power and its toughness is equal to that creature's toughness.

Kalastria Highborn

Whenever this creature or another Vampire you control dies, you may pay {B}. If you do, target player loses 2 life and you gain 2 life.