Gill Grunt was a brave soul who joined the Gillmen military in search of adventure. While journeying through a misty lagoon in the clouds, he met an enchanting mermaid. He vowed to return to her after his tour. Keeping his promise, he came back to the lagoon years later, only to learn a nasty band of pirates had kidnapped the mermaid. Heartbroken, Gill Grunt began searching all over Skylands. Though he had yet to find her, he joined the Skylanders to help protect others from such evil, while still keeping an ever-watchful eye for the beautiful mermaid and the pirates who took her.
Gill Grunt Series 2 - Metallic Green is a special paint variant of Gill Grunt Series 2 appearing in Giants. He was given away at the GameStop Expo in 2013. He is one of several special paint variant Skylanders to be given away at trade shows.
Other trade show figures are Cynder - Metallic Purple (Toy Fair NYC 2012), Spyro - Chrome (E3 2012), Hex - Pearl (Toy Fair Nuremberg 2012), Chop Chop - Metallic Blue (Toy Fair NYC 2013), Hot Dog - Color Shift (E3 2013), Dune Bug - Metallic Red (Toy Fair NYC 2014).
This same figure was pictured in the Toys R Us holiday ads as a reward for spending over $100 on Skylanders during the holidays. However to my knowledge no one has received this figure yet. Toys R Us employees have told me that coupons for the figure are supposed to go out to those who qualify between 1/17/2014 and 1/31/2014.
Here is an image from the ad: