Stromling Pirates were formerly members of Captain Jack Knife's crew of Pirates in Gnarled Forest. When the greedy Pirates stockpiled Maelstrom Crystals under the mistaken belief that they were treasure, the Kraken attacked the Black Seas Barracuda and threw it into a tree. Jack Knife and his pirates quickly moved the Infected Treasure Chests inland, but not before the Maelstrom corrupted most of his crew into Stromling Pirates and Admirals.
Stromling Pirates also appear in the Great Minifig Mission. In Mission 12, Stromling Pirates are identified based upon their origin and risk level, and then they appear as targets throughout a town modeled after Zorillo Plaza. Their unpredictable risk level plays a role in the second puzzle of Mission 20.
Stromling Pirates spawn in great numbers at the Maelstrom Trench. A number of Stromling Pirates spawn in the forestry near Elephant Escarpment. In Brig Rock, Stromling Pirates emerge from cracks in the rock walls of the wrecked prison, but their entrance can be delayed by blocking the cracks with Barricades. Stromling Pirates lumber towards nearby players and attack with the two cutlasses fused to their left hands. Although Stromling Pirates only have 8 Life and are the weakest Stromlings in Gnarled Forest, they find their strength in numbers and can easily overtake and overwhelm players. However, as discovered by Renee Tombcrusher, Stromling Pirates can be mesmerized by nearby Siren Stunners, allowing players to easily attack the stupefied Stromlings.
Stromling Pirates makes a cameo appearance during the races held at Dragonmaw Chasm in Forbidden Valley. When players drive through the Stromling-infested tunnels underneath Paradox Refinery, Stromling Pirates can be glimpsed watching the race from either side of the tunnel, cheering alongside Stromlings.
Cutlass Slash: The Stromling Pirate makes several slashes in quick succession with the two cutlasses attached to his hand, each dealing 1 damage.
Downward Slash: The Stromling Pirate takes a hard swing, dealing 2 damage and embedding his sword in the ground, temporarily immobilizing him.
In alpha testing, Stromling Pirates were known as Darkling Pirates. An early developmental screenshot of a Darkling Pirate extracted by the Bradford Rant Institute of Cosmic Kinesis from Pod 4 shows that they were originally more purple in hue. In alpha testing, Darkling Pirates had different textures that had a simpler design in comparison to the finalized version. Until mid-beta testing, Stromling Pirates had a deep-pitched scream upon being smashed. In beta testing, Stromling Pirates were considerably weaker than their released version.
In alpha testing, Darkling Pirates made an appearance in the Gnarled Forest Survival, in which they could spawn around the Battle Trench in massive numbers.
Stromling Pirates appear to be the successors of Evil Pirates, which were enemy pirates in pre-alpha versions of LEGO Universe.