Food Chain

Exile a creature you control: Add X mana of any one color, where X is 1 plus the exiled creature's mana value. Spend this mana only to cast creature spells.

Squee, the Immortal

You may cast Squee, the Immortal from your graveyard or from exile.

Aluren

Any player may cast creature spells with mana value 3 or less without paying their mana costs and as though they had flash.

Phyrexian Altar

Sacrifice a creature: Add one mana of any color.

Ashnod's Altar

Goblin Bombardment

Sacrifice a creature: Goblin Bombardment deals 1 damage to any target.

Eternal Scourge

You may cast Eternal Scourge from exile.
When Eternal Scourge becomes the target of a spell or ability an opponent controls, exile Eternal Scourge.