Borborygmos and Fblthp

Whenever Borborygmos and Fblthp enters the battlefield or attacks, draw a card, then you may discard any number of land cards. When you discard one or more cards this way, Borborygmos and Fblthp deals twice that much damage to target creature.
{1}{U}: Put Borborygmos and Fblthp into its owner's library third from the top.

Inquisitor's Flail

If equipped creature would deal combat damage, it deals double that damage instead.
If another creature would deal combat damage to equipped creature, it deals double that damage to equipped creature instead.
Equip {2}

Dictate of the Twin Gods

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

Goblin Goliath

When Goblin Goliath enters the battlefield, create a number of 1/1 red Goblin creature tokens equal to the number of opponents you have.
{3}{R}, {T}: If a source you control would deal damage to an opponent this turn, it deals double that damage to that player instead.