Rakdos Guildgate

Rakdos Guildgate enters tapped.
{T}: Add {B} or {R}.

The Balrog, Durin's Bane

This spell costs {1} less to cast for each permanent sacrificed this turn.
Haste
The Balrog, Durin's Bane can't be blocked except by legendary creatures.
When The Balrog dies, destroy target artifact or creature an opponent controls.

Hagra Constrictor

Hagra Constrictor enters with two +1/+1 counters on it.
Each creature you control with a +1/+1 counter on it has menace. (A creature with menace can't be blocked except by two or more creatures.)

Mountain

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Dragonlord Kolaghan

Flying, haste
Other creatures you control have haste.
Whenever an opponent casts a creature or planeswalker spell with the same name as a card in their graveyard, that player loses 10 life.

Infernal Scarring

Enchant creature
Enchanted creature gets +2/+0 and has "When this creature dies, draw a card."

Maniacal Rage

Enchant creature
Enchanted creature gets +2/+2 and can't block.

Immersturm Predator

Flying
Whenever Immersturm Predator becomes tapped, exile up to one target card from a graveyard and put a +1/+1 counter on Immersturm Predator.
Sacrifice another creature: Immersturm Predator gains indestructible until end of turn. Tap it.

Rakdos Cackler

Unleash (You may have this creature enter with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.)

Dreadhorde Butcher

Haste
Whenever Dreadhorde Butcher deals combat damage to a player or planeswalker, put a +1/+1 counter on Dreadhorde Butcher.
When Dreadhorde Butcher dies, it deals damage equal to its power to any target.

Ashenmoor Liege

Other black creatures you control get +1/+1.
Other red creatures you control get +1/+1.
Whenever Ashenmoor Liege becomes the target of a spell or ability an opponent controls, that player loses 4 life.

Koth, Fire of Resistance

+2: Search your library for a basic Mountain card, reveal it, put it into your hand, then shuffle.
−3: Koth, Fire of Resistance deals damage to target creature equal to the number of Mountains you control.
−7: You get an emblem with "Whenever a Mountain you control enters, this emblem deals 4 damage to any target."