Volcanic Geyser

Volcanic Geyser deals X damage to any target.

Fireball

This spell costs {1} more to cast for each target beyond the first.
Fireball deals X damage divided evenly, rounded down, among any number of targets.

Seeker of Skybreak

Rosheen Meanderer

{T}: Add {C}{C}{C}{C}. Spend this mana only on costs that contain {X}.

Thrive

Put a +1/+1 counter on each of X target creatures.

Horizon Stone

If you would lose unspent mana, that mana becomes colorless instead.

Ice Cauldron

{X}, {T}: You may exile a nonland card from your hand. You may cast that card for as long as it remains exiled. Put a charge counter on Ice Cauldron and note the type and amount of mana spent to pay this activation cost. Activate only if there are no charge counters on Ice Cauldron.
{T}, Remove a charge counter from Ice Cauldron: Add Ice Cauldron's last noted type and amount of mana. Spend this mana only to cast the last card exiled with Ice Cauldron.