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.

Mass Manipulation

Gain control of X target creatures and/or planeswalkers.

Comet Storm

Multikicker {1} (You may pay an additional {1} any number of times as you cast this spell.)
Choose any target, then choose another target for each time this spell was kicked. Comet Storm deals X damage to each of them.

Electrodominance

Electrodominance deals X damage to any target. You may cast a spell with mana value X or less from your hand without paying its mana cost.

Storm King's Thunder

When you next cast an instant or sorcery spell this turn, copy that spell X times. You may choose new targets for the copies.

Elementalist's Palette

Whenever you cast a spell with {X} in its mana cost, put two charge counters on Elementalist's Palette.
{T}: Add one mana of any color.
{T}: Add {C} for each charge counter on Elementalist's Palette. Spend this mana only on costs that contain {X}.

Commander's Insight

Target player draws X cards plus an additional card for each time they've cast a commander from the command zone this game.

Blue Sun's Zenith

Target player draws X cards. Shuffle Blue Sun's Zenith into its owner's library.