Legionnaire of Doom is an achievement from Plants vs. Zombies: Garden Warfare. To earn it, the player must plant a Doom-shroom, a Bamboo Shoot, a Fire Peashooter and an Ice Peashooter. However, the player does not have to plant them in one session.
Legionnaire of Doom is very easy to get, as the player does not have to plant them in one session. The only thing you need to do is get them in sticker packs. Once you have done that, you can play Garden Ops, Taco Bandits, or Gardens & Graveyards, plant them somewhere, and you will earn the achievement.