Goblin King

Other Goblins get +1/+1 and have mountainwalk.

Goblin Balloon Brigade

{R}: Goblin Balloon Brigade gains flying until end of turn.

Dragon Whelp

Flying
{R}: Dragon Whelp gets +1/+0 until end of turn. If this ability has been activated four or more times this turn, sacrifice Dragon Whelp at the beginning of the next end step.

Detonate

Destroy target artifact with mana value X. It can't be regenerated. Detonate deals X damage to that artifact's controller.

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Stone Giant

{T}: Target creature you control with toughness less than Stone Giant's power gains flying until end of turn. Destroy that creature at the beginning of the next end step.

Fire Elemental

Earthquake

Earthquake deals X damage to each creature without flying and each player.

Mountain

Blood Moon

Atog

Sacrifice an artifact: Atog gets +2/+2 until end of turn.

Fireball

This spell costs {1} more to cast for each target beyond the first.
Fireball deals X damage divided evenly, rounded down, among any number of targets.

Mana Clash

You and target opponent each flip a coin. Mana Clash deals 1 damage to each player whose coin comes up tails. Repeat this process until both players' coins come up heads on the same flip.

Kobold Taskmaster

Other Kobold creatures you control get +1/+0.

Ball Lightning

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Haste (This creature can attack and {T} as soon as it comes under your control.)
At the beginning of the end step, sacrifice this creature.

Iron Star

Whenever a player casts a red spell, you may pay {1}. If you do, you gain 1 life.