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