Ancient Imperiosaur

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.)
Trample, ward {2}
Ancient Imperiosaur enters with two +1/+1 counters on it for each creature that convoked it.

Mountain

Kuldotha Rebirth

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

Forbidden Friendship

Create a 1/1 red Dinosaur creature token with haste and a 1/1 white Human Soldier creature token.

Forest

Burning-Tree Emissary

When Burning-Tree Emissary enters, add {R}{G}.

Ornithopter

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.")

Reckless Bushwhacker

Surge {1}{R} (You may cast this spell for its surge cost if you or a teammate has cast another spell this turn.)
Haste
When Reckless Bushwhacker enters, if its surge cost was paid, other creatures you control get +1/+0 and gain haste until end of turn.

Game Trail

As Game Trail enters, you may reveal a Mountain or Forest card from your hand. If you don't, Game Trail enters tapped.
{T}: Add {R} or {G}.

Gleeful Demolition

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

Arboretum Elemental

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.)
Hexproof (This creature can't be the target of spells or abilities your opponents control.)