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