Shadowborn Apostle

A deck can have any number of cards named Shadowborn Apostle.
{B}, Sacrifice six creatures named Shadowborn Apostle: Search your library for a Demon creature card, put it onto the battlefield, then shuffle.

Hellcarver Demon

Flying
Whenever Hellcarver Demon deals combat damage to a player, sacrifice all other permanents you control and discard your hand. Exile the top six cards of your library. You may cast any number of spells from among cards exiled this way without paying their mana costs.

Tibalt's Trickery

Counter target spell. Choose 1, 2, or 3 at random. Its controller mills that many cards, then exiles cards from the top of their library until they exile a nonland card with a different name than that spell. They may cast that card without paying its mana cost. Then they put the exiled cards on the bottom of their library in a random order.

Emergent Ultimatum

Search your library for up to three monocolored cards with different names and exile them. An opponent chooses one of those cards. Shuffle that card into your library. You may cast the other cards without paying their mana costs. Exile Emergent Ultimatum.

Snow-Covered Swamp

Omniscience

You may cast spells from your hand without paying their mana costs.

Kenrith, the Returned King

{R}: All creatures gain trample and haste until end of turn.
{1}{G}: Put a +1/+1 counter on target creature.
{2}{W}: Target player gains 5 life.
{3}{U}: Target player draws a card.
{4}{B}: Put target creature card from a graveyard onto the battlefield under its owner's control.

Ugin, the Spirit Dragon

+2: Ugin, the Spirit Dragon deals 3 damage to any target.
−X: Exile each permanent with mana value X or less that's one or more colors.
−10: You gain 7 life, draw seven cards, then put up to seven permanent cards from your hand onto the battlefield.

Burning-Rune Demon

Flying
When Burning-Rune Demon enters, you may search your library for exactly two cards not named Burning-Rune Demon that have different names. If you do, reveal those cards. An opponent chooses one of them. Put the chosen card into your hand and the other into your graveyard, then shuffle.

Withengar Unbound

Flying, intimidate, trample (A creature with intimidate can't be blocked except by artifact creatures and/or creatures that share a color with it.)
Whenever a player loses the game, put thirteen +1/+1 counters on Withengar Unbound.

Elbrus, the Binding Blade

Equipped creature gets +1/+0.
When equipped creature deals combat damage to a player, unattach Elbrus, the Binding Blade, then transform it.
Equip {1}

Elbrus, the Binding Blade // Withengar Unbound

Exalted Flamer of Tzeentch

Sorcerous Inspiration — At the beginning of your upkeep, return an instant or sorcery card at random from your graveyard to your hand.
Fire of Tzeentch — Whenever you cast an instant or sorcery spell, Exalted Flamer of Tzeentch deals 1 damage to each opponent.

Kozilek, Butcher of Truth

When you cast this spell, draw four cards.
Annihilator 4 (Whenever this creature attacks, defending player sacrifices four permanents.)
When Kozilek, Butcher of Truth is put into a graveyard from anywhere, its owner shuffles their graveyard into their library.

Archfiend of Despair

Flying
Your opponents can't gain life.
At the beginning of each end step, each opponent loses life equal to the life that player lost this turn. (Damage causes loss of life.)

Demonlord Belzenlok

Flying, trample
When Demonlord Belzenlok enters, exile cards from the top of your library until you exile a nonland card, then put that card into your hand. If the card's mana value is 4 or greater, repeat this process. Demonlord Belzenlok deals 1 damage to you for each card put into your hand this way.

Mountain

Genesis Ultimatum

Look at the top five cards of your library. Put any number of permanent cards from among them onto the battlefield and the rest into your hand. Exile Genesis Ultimatum.