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