The Bloodlions and the Battlewolves were the only two tribes of Orcs that joined the Plague Queen. However, those two tribes see eachother as mortal enemies, and Skoll is the leader of the Battlewolves at this time. 

    Eager to prove himself and his leadership ability, Skoll wanted to perform something grand. Tricked by evil forces, Skoll poisoned the World Tree guarded by Karen, Pan and Thera. It was not until the Prime Evils were unsealed did Skoll realize his terrible mistake.