The Illuminator is a magical glowing horn created by the Skylander, Whirlwind. She enchanted this crystal horn to bring eternal daylight to the Frost Elves of Winter Keep after their land fell under a curse of eternal midnight. Not only did the Illuminator break the curse, but also gave the Frost Elves courage.
During the attack on Winter Keep in Skylanders: Swap Force, the Illuminator became encased in ice by an Ice Geargolem, causing its light to stop working and shrouding the keep in darkness. The Skylanders eventually and quickly defeated the Geargolem, before melting the ice around the Illuminator to allow its light to shine throughout the land once more.
When the Skylanders helped save Winter Keep, the Frost Elves provided them with the Illuminator which was needed to help the heroes see their way through the blizzard-infested areas of the Frostfest Mountains. Once there, the Illuminator's light guided the Skylanders through the thick blizzard surrounding the mountain.