Mango Tango is an achievement in Plants vs. Zombies: Garden Warfare 2. To earn it, the player must complete the mission named "Showdown," which is the last mission that Agent Citron gives to the player.
This should be simple to get. Just go talk to Ironball, defeat the key holder, grab the key, free Ironball, and then go defeat the S.H.R.IMP mech. If the player has any difficulty, lower the difficulty to make it easier. Using a strong character such as Agent Pea can also help. Then, report to Agent Citron.