Sunburst is a keyword ability.
It is a static ability that means the affected spell will enter the battlefield with an additional number of +1/+1 counters (for creature spells), or charge counters (for non-creature spells) equal to the number of different colors of mana spent to cast it.
Abby has cast a Suntouched Myr and has spent to cast it, it will enter the battlefield with an additional two +1/+1 counters as two different colours of mana were spent to cast it.
Later in the game Abby casts a Pentad Prism for , as this is a non-creature spell, it will enter the battlefield with two charge counters on it, rather than +1/+1 counters.
- 702.43a. Sunburst is a static ability that functions as an object is entering the battlefield from the stack. "Sunburst" means "If this object is entering the battlefield from the stack as a creature, it enters the battlefield with a +1/+1 counter on it for each color of mana spent to cast it. If this object is entering the battlefield from the stack and isn't entering the battlefield as a creature, it enters the battlefield with a charge counter on it for each color of mana spent to cast it."
- 702.43b. Sunburst applies only as the spell is resolving and only if one or more colored mana was spent on its costs. Mana paid for additional or alternative costs applies.
- 702.43c. 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.
- 702.43d. If an object has multiple instances of sunburst, each one works separately.