Frenzied Goblin

Whenever Frenzied Goblin attacks, you may pay {R}. If you do, target creature can't block this turn.

Chain Lightning

Chain Lightning deals 3 damage to any target. Then that player or that permanent's controller may pay {R}{R}. If the player does, they may copy this spell and may choose a new target for that copy.

Kird Ape

Kird Ape gets +1/+2 as long as you control a Forest.

Forest

Sure Strike

Target creature gets +3/+0 and gains first strike until end of turn.

Burning-Tree Emissary

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

Raking Claws

Target creature gains double strike until end of turn.
Cycling {2} ({2}, Discard this card: Draw a card.)

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Giant Growth

Target creature gets +3/+3 until end of turn.

Rancor

Enchant creature
Enchanted creature gets +2/+0 and has trample.
When Rancor is put into a graveyard from the battlefield, return Rancor to its owner's hand.

Mountain

Monastery Swiftspear

Haste
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Manamorphose

Add two mana in any combination of colors.
Draw a card.

Boulder Rush

Target creature gets +2/+0 until end of turn. (Then exile this card. You may cast the creature later from exile.)