Sunburst

Sunburst is a keyword ability appearing on both artifacts and artifact creatures that puts charge and +1/+1 counters, respectively, on the card when it comes into play. The number of counters is equal to the number of different colors of mana used to play the spell.

In addition, Sunburst can also be used as a sort of 'X-value'. One card, Arcbound Wanderer has the ability "Modular-Sunburst". "Modular-Sunburst" means that the creature comes into play with a +1/+1 counter on it for each color of mana payed to play it, and when that creature is put into a graveyard from play, the controller may move the +1/+1 counters onto another artifact creature.

All tournament-legal cards with sunburst first appeared in Fifth Dawn.

From the Comprehensive Rules:

• 502.37. Sunburst
  • 502.37a Sunburst is a static ability that functions as an object is coming into play from the stack. “Sunburst” means “If this object is coming into play from the stack as a creature, it comes into play with a +1/+1 counter on it for each color of mana used to pay its cost. If this object is coming into play from the stack and isn’t coming into play as a creature, it comes into play with a charge counter on it for each color of mana used to pay its cost.”
  • 502.37b Sunburst applies only as the spell is resolving and only if one or more colored mana was paid for its costs. Mana paid for additional or alternative costs applies.
  • 502.37c Sunburst can also be used to set a variable number for another ability. If the keyword is used in this way, it doesn’t matter whether the ability is on a creature spell or on a noncreature spell.
  • 502.37d If an object has multiple instances of sunburst, each one works separately.