Army Men III is an indie game it follows the first three games.
This is from the site:
Since the death of Major Mylar, the Tan army has lost every battle. Even with the help of the Blue and Grey armies, it seems that the Green are destined to win and the war finally appears to be coming to an end after so many years.
Unbeknownst to the Green however, The Insane Grey Doctor who was recently declared MIA, is still alive and has been furthering his research that he started back in the tropical zone of the plastic world, going beyond zombies and instead has found a new interest in the insects of the real world. Spawning creature after creature of the vilest order, The Grey Doctor's power only grows with each passing moment.
Seeking to capture and destroy the plastic world, The Doctor finally emerges back in the real world, with his new found army ready and at his command he launches an assault on all of the nations. But unknown to anyone, even Plastro himself, the Grey Doctor has also recovered Major Mylar’s remains and with them, has created a weapon so powerful, it threatens the balance of both the real and the plastic worlds...</stron