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