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