Engineered Explosives

Sunburst (This enters with a charge counter on it for each color of mana spent to cast it.)
{2}, Sacrifice Engineered Explosives: Destroy each nonland permanent with mana value equal to the number of charge counters on Engineered Explosives.

Mystery Booster 2

Double Masters

Sunburst (This enters the battlefield with a charge counter on it for each color of mana spent to cast it.)
{2}, Sacrifice Engineered Explosives: Destroy each nonland permanent with converted mana cost equal to the number of charge counters on Engineered Explosives.

Ultimate Box Topper

Sunburst
{2}, Sacrifice Engineered Explosives: Destroy each nonland permanent with converted mana cost equal to the number of charge counters on Engineered Explosives.

Ultimate Masters

Kaladesh Inventions

Colorless mana won't give Engineered Explosives another charge counter. Colorless is not a color.

If a permanent has {X} in its mana cost, X is considered to be 0.

Tokens that aren't a copy of something else don't have a mana cost. Anything without a mana cost normally has a mana value of 0.

You can choose any value for X as you cast Engineered Explosives. The value chosen for X doesn't directly affect the number of charge counters Engineered Explosives enters the battlefield with, but it does let you pay more mana and thus spend more colors of mana to cast it.