Chain Reaction

Chain Reaction deals X damage to each creature, where X is the number of creatures on the battlefield.

Mana Flare

Whenever a player taps a land for mana, that player adds one mana of any type that land produced.

Furnace of Rath

If a source would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Screaming Nemesis

Haste
Whenever Screaming Nemesis is dealt damage, it deals that much damage to any other target. If a player is dealt damage this way, they can't gain life for the rest of the game.

Fiery Inscription

When Fiery Inscription enters, the Ring tempts you.
Whenever you cast an instant or sorcery spell, Fiery Inscription deals 2 damage to each opponent.

Snow-Covered Mountain

Powerbalance

Whenever an opponent casts a spell, you may reveal the top card of your library. If you do, you may cast that card without paying its mana cost if the two spells have the same mana value.