Mountain

Grishnákh, Brash Instigator

When Grishnákh, Brash Instigator enters, amass Orcs 2. When you do, until end of turn, gain control of target nonlegendary creature an opponent controls with power less than or equal to the amassed Army's power. Untap that creature. It gains haste until end of turn.

Goblin Fireleaper

{1}{R}: Goblin Fireleaper gets +1/+0 until end of turn.
When Goblin Fireleaper dies, it deals damage equal to its power to target creature an opponent controls.

Siege-Gang Commander

When Siege-Gang Commander enters, create three 1/1 red Goblin creature tokens.
{1}{R}, Sacrifice a Goblin: Siege-Gang Commander deals 2 damage to any target.

Olog-hai Crusher

Trample
Olog-hai Crusher can't block unless you control a Goblin or Orc.

Warbeast of Gorgoroth

Whenever Warbeast of Gorgoroth or another creature you control with power 4 or greater dies, amass Orcs 2. (Put two +1/+1 counters on an Army you control. It's also an Orc. If you don't control an Army, create a 0/0 black Orc Army creature token first.)

Foray of Orcs

Amass Orcs 2. When you do, Foray of Orcs deals X damage to target creature an opponent controls, where X is the amassed Army's power. (To amass Orcs 2, put two +1/+1 counters on an Army you control. It's also an Orc. If you don't control an Army, create a 0/0 black Orc Army creature token first.)

Assault on Osgiliath

Amass Orcs X, then Goblins and Orcs you control gain double strike and haste until end of turn. (To amass Orcs X, put X +1/+1 counters on an Army you control. It's also an Orc. If you don't control an Army, create a 0/0 black Orc Army creature token first.)

Spiteful Banditry

When Spiteful Banditry enters, it deals X damage to each creature.
Whenever one or more creatures your opponents control die, you create a Treasure token. This ability triggers only once each turn.

Thrill of Possibility

As an additional cost to cast this spell, discard a card.
Draw two cards.

Oliphaunt

Trample
Whenever Oliphaunt attacks, another target creature you control gets +2/+0 and gains trample until end of turn.
Mountaincycling {1} ({1}, Discard this card: Search your library for a Mountain card, reveal it, put it into your hand, then shuffle.)

Moria Marauder

Double strike
Whenever a Goblin or Orc you control deals combat damage to a player, exile the top card of your library. You may play that card this turn.

Faithless Looting

Draw two cards, then discard two cards.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Improvised Club

As an additional cost to cast this spell, sacrifice an artifact or creature.
Improvised Club deals 4 damage to any target.

Orcish Siegemaster

Trample
Other Orcs and Goblins you control have trample.
Whenever Orcish Siegemaster attacks, it gets +X/+0 until end of turn, where X is the greatest power among creatures you control.

Book of Mazarbul

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Amass Orcs 1. (Put a +1/+1 counter on an Army you control. It's also an Orc. If you don't control an Army, create a 0/0 black Orc Army creature token first.)
II — Amass Orcs 2.
III — Creatures you control get +1/+0 and gain menace until end of turn.