Juxtapose

You and target player exchange control of the creature you each control with the greatest mana value. Then exchange control of artifacts the same way. If two or more permanents a player controls are tied for greatest, their controller chooses one of them.

Homarid Spawning Bed

{1}{U}{U}, Sacrifice a blue creature: Create X 1/1 blue Camarid creature tokens, where X is the sacrificed creature's mana value.

Energy Tap

Tap target untapped creature you control. If you do, add an amount of {C} equal to that creature's mana value.

Lunar Insight

Draw a card for each different mana value among nonland permanents you control.

Sacrifice

As an additional cost to cast this spell, sacrifice a creature.
Add an amount of {B} equal to the sacrificed creature's mana value.

Pyre of Heroes

{2}, {T}, Sacrifice a creature: Search your library for a creature card that shares a creature type with the sacrificed creature and has mana value equal to 1 plus that creature's mana value. Put that card onto the battlefield, then shuffle. Activate only as a sorcery.

Anchor to Reality

As an additional cost to cast this spell, sacrifice an artifact or creature.
Search your library for an Equipment or Vehicle card, put that card onto the battlefield, then shuffle. If it has mana value less than the sacrificed permanent's mana value, scry 2.

Morbid Curiosity

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw cards equal to the mana value of the sacrificed permanent.

Narfi, Betrayer King

Other snow and Zombie creatures you control get +1/+1.
{S}{S}{S}: Return this card from your graveyard to the battlefield tapped. ({S} can be paid with one mana from a snow source.)

Soul Shatter

Each opponent sacrifices a creature or planeswalker with the greatest mana value among creatures and planeswalkers they control.

Reckoner's Bargain

As an additional cost to cast this spell, sacrifice an artifact or creature.
You gain life equal to the sacrificed permanent's mana value. Draw two cards.