Major Mylar is the main antagonist of Army Men II
He attempted to lead a coup against General Plastro, but he failed when he was defeated by Sarge and his men.
Major Mylar is only ever seen twice; once at the start of the campaign, and then at the ending, where he is fought against. It can be assumed he leads a rogue faction of Tan soldiers against General Plastro, though his reasoning for doing so is largely unknown. The relationship between Major Mylar and his forces with the Tan Republic is largely unknown; he destroys the portal behind General Plastro so he cannot return to the Plastic World, yet still engages Sarge and the Green Nation in combat.
Army Men II
Major Mylar is the overarching main antagonist of Army Men II. When he first appears, he seals General Plastro inside of the Real World with Sarge by detonating the portal once he enters. He does not appear for the rest of the campaign, and it is unknown if the Tan forces Sarge battles against are part of Mylar’s faction, or Plastro’s.
It is possible that he shares beliefs with the renegade Green Colonel, that believes the Army Men were not real and conflict between all nations must come to an end by killing all the soldiers, but this idea is never expanded upon. It is likely that Mylar directly influenced the Green Colonel with his own beliefs. But none of this is known for sure.
During the final mission of Army Men II, he takes shelter in a castle playset, alongside a large army of soldiers loyal to his cause. He is finally confronted in the final level, utilizing a large cannon that lobs mortar shells at Sarge and his men. After a hard fought battle, Sarge is able to defeat him. In a last ditch effort, Major Mylar attempts to toss a grenade at Sarge; however, his arm melts off with the fire provoked by the battle before he is able to throw it, and the grenade detonates below Mylar, seemingly killing him into pieces.
At some point after this battle, the Grey scientist, Dr. Madd, is seen piecing the shattered remains of Mylar back together.
Despite the teaser at the end of Army Men II, Major Mylar does not make a reappearance throughout the entire Army Men history again.