Mountain

Castle Embereth

Castle Embereth enters tapped unless you control a Mountain.
{T}: Add {R}.
{1}{R}{R}, {T}: Creatures you control get +1/+0 until end of turn.

Regal Leosaur

Mutate {1}{R/W}{R/W} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Whenever this creature mutates, other creatures you control get +2/+1 until end of turn.

Rugged Prairie

{T}: Add {C}.
{R/W}, {T}: Add {R}{R}, {R}{W}, or {W}{W}.

Knight-Errant of Eos

Convoke
When Knight-Errant of Eos enters, look at the top six cards of your library. You may reveal up to two creature cards with mana value X or less from among them, where X is the number of creatures that convoked Knight-Errant of Eos. Put the revealed cards into your hand, then shuffle.

Battlefield Forge

{T}: Add {C}.
{T}: Add {R} or {W}. Battlefield Forge deals 1 damage to you.

Memnite

Kuldotha Rebirth

As an additional cost to cast this spell, sacrifice an artifact.
Create three 1/1 red Goblin creature tokens.

Halo Hopper

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)

Ornithopter

Goblin Bushwhacker

Kicker {R} (You may pay an additional {R} as you cast this spell.)
When Goblin Bushwhacker enters, if it was kicked, creatures you control get +1/+0 and gain haste until end of turn.

Venerated Loxodon

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
When Venerated Loxodon enters, put a +1/+1 counter on each creature that convoked it.

Gleeful Demolition

Destroy target artifact. If you controlled that artifact, create three 1/1 red Phyrexian Goblin creature tokens.

Thraben Inspector

When Thraben Inspector enters, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Voldaren Epicure

When Voldaren Epicure enters, it deals 1 damage to each opponent. Create a Blood token. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this artifact: Draw a card.")