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.

Mountain

Shock

Banefire

Banefire deals X damage to any target.
If X is 5 or more, this spell can't be countered and the damage can't be prevented.

Obosh, the Preypiercer

Companion — Your starting deck contains only cards with odd mana values and land cards. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.)
If a source you control with an odd mana value would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Swamp

Fire Servant

If a red instant or sorcery spell you control would deal damage, it deals double that damage instead.