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