The Heavy Destroyer Snake is found on level level. Have bombs, cannons, and other "red" weapons for the fight. The snake has a very large rotation angle. Use all your bombs and cannons on it. If it survived, use normal guns. You only have a few seconds before he turns and begins hits "metal rain" attack. Run and wait for another chance to strike, then repeat the process.
Have armor breaking Pfaust or Canguns, as well as a Minigun equipped. You will also need explosives (Nailbombs recommended). As far as defense, 150 health, 100 armor, and a Magshield is recommended. Finally, have a Teleporter. Start by running into the Boss room and fire a few of armor-breaking Pfaust and/or Canguns. Then, switch to the Minigun and aim for the piece of Boss armor that you hit with the artillery earlier. When the outer layer breaks, equip the Nailbombs then run in and drop them close to the inner layer of armor. Quickly swap to the next batch of explosives and drop them as well. Blow up yourself as well as the Boss then respawn in the next room.
On level 5 have two PzFaust Ap. Give one to each of the two robots. PzFaust Ap is very useful against robots. It is important not to miss.
Play Arena 1. Choose the weapon set you are best skilled with and go through the arena levels. Starting at levels 4 or 5, the amount of enemies will be enough for 100 shots. Try to gather the enemies into groups, take them to narrow corridors or small rooms where you can maneuver. Try to be accurate.