Fast Reload:
Instead of reloading normal just quickly switch weapons back and forth.
Unlock Characters:
Beat the level on Medium difficulty to unlock these characters:
2280 Return to Planet X: Ozor Mox
2019 NeoTokyo: Sadako
1853 Wild West: The Colonel
1972 Atom Smasher: Khallos
1920 Aztec Ruins: Stone Golem
1990 Siberia: Hybrid Mutant
1938 Chicago: Big Tony
1895 Notre Dame: Jacque de la Morte
2280 Return to Planet X: Ozor Mox
2019 NeoTokyo: Sadako
2315 Robot Factory: Machinist
2401 SpaceStation: Berserker Splitter
Unlock Multiplayer Maps:
Scrapyard: Clear Arcade League - Amateur League - Mode Madness - Scrap Medal with a Bronze Medal or higher
Nightclub: Clear Arcade League - Amateur League - Too Hot to Handle - Disco Inferno with a Broze Medal or higher
Hangar: Clear Arcade League - Amateur League - Beginner's Series - Top Shot with a Bronze Medal or higher
Robot Factory: Clear Arcade League - Amateur League - It's a Blast - Demolition Derby with a Bronze Medal or higher
Ufopia: Clear Arcade League - Honorary League - Maximus - Cold Corpse Caper with a Bronze Medal or higher
Chinese: Clear Arcade League - Honorary Leauge - Elimination Series - Starship Whoopers with a Bronze Medal or higher
Chasm: Clear Arcade League - Honorary League - Outnumbered but Never Outpunned - Can't Handle This with a Bronze Madal or Higher
Streets: Clear Spaceship: 2401 on the Easy difficulty setting
Compund: Clear Spaceship: 2401 on the Normal difficulty setting
Site: Linked to amount of Arcade League matches or Challenges completed
Circus: Clear Challenge - Monkeying Around - Dam Bursters with a Bronze Medal.