Jaya's Immolating Inferno

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Jaya's Immolating Inferno deals X damage to each of up to three targets.

Ingenious Prodigy

Skulk (This creature can't be blocked by creatures with greater power.)
Ingenious Prodigy enters with X +1/+1 counters on it.
At the beginning of your upkeep, if Ingenious Prodigy has one or more +1/+1 counters on it, you may remove a +1/+1 counter from it. If you do, draw a card.

Doppelgang

For each of X target permanents, create X tokens that are copies of that permanent.

Blue Sun's Twilight

Gain control of target creature with mana value X or less. If X is 5 or more, create a token that's a copy of that creature.

Patriar's Seal

{T}: Add one mana of any color.
{1}, {T}: Untap target legendary creature you control.

The Goose Mother

Flying
The Goose Mother enters with X +1/+1 counters on it.
When The Goose Mother enters, create half X Food tokens, rounded up.
Whenever The Goose Mother attacks, you may sacrifice a Food. If you do, draw a card.

Freed from the Real

Enchant creature
{U}: Tap enchanted creature.
{U}: Untap enchanted creature.

Thousand-Year Elixir

You may activate abilities of creatures you control as though those creatures had haste.
{1}, {T}: Untap target creature.

Rampaging Yao Guai

Vigilance, trample
Rampaging Yao Guai enters with X +1/+1 counters on it.
When Rampaging Yao Guai enters, destroy any number of target artifacts and/or enchantments with total mana value X or less.

Wave Goodbye

Return each creature without a +1/+1 counter on it to its owner's hand.

Open the Way

X can't be greater than the number of players in the game.
Reveal cards from the top of your library until you reveal X land cards. Put those land cards onto the battlefield tapped and the rest on the bottom of your library in a random order.

Hell to Pay

Hell to Pay deals X damage to target creature. Create a number of tapped Treasure tokens equal to the amount of excess damage dealt to that creature this way.

Multiple Choice

If X is 1, scry 1, then draw a card.
If X is 2, you may choose a player. They return a creature they control to its owner's hand.
If X is 3, create a 4/4 blue and red Elemental creature token.
If X is 4 or more, do all of the above.