Here is the full list of all 28 MeltDown achievements.
Complete 10 online games.
Collect 5000 Coins.
Destroy 1000 bots.
Finish an online game.
Finish an online game with 4 players.
Destroy 30 bots with the Shotgun.
Upgrade a weapon to the maximum level.
Pickup 10 Nukes.
Obtain a 3 star rank on a mission.
Destroy 30 bots with a melee weapon.
Melee Kill a Fuel Bot.
Complete a mission in less than 2 minutes.
Complete a mission without losing any health.
Finish tutorial.
Own all weapons.
Max out all skills.
Destroy an enemy of each type.
Destroy 30 bots with the Flamer.
Destroy 30 bots with the Shocker.
Collect 100 Chips.
Reach 100% Critical Strike with the Fury skill.
Destroy 30 bots with the Grenade or Rocket Launcher.
Do a Multi-Kill.
Get Level 1 Prestige
Get Level 3 Prestige
Destroy The Barrager
Destroy The Enforcer
Destroy The Electrocutioner