Greenskin paces up and down the deck of his ship, and it's difficult (but not impossible) to pull him without also attracting his minions. Take caution on the trash pulls just prior to Greenskin; it is very easy to accidentally pull Greenskin as well. When fighting against him and his minions, sap and polymorph adds, and focus on Greenskin. Tank also should keep Greenskin away from casters because of his cleave.
Abilties
Poisoned Harpoon - Inflicts normal damage plus 30 to an enemy, then an additional 45 Nature damage every 10 sec. for 1 min.
Cleave - Inflicts 110% of normal melee damage to an enemy and its nearest ally.