Blazing Chrome

The trick with this achievement is using the Orange Mech's laser weapon properly. The temptation is to hold down 'X' and shoot the charged laser continuously until it is depleted.
Instead you should basically just tap 'X' to fire the laser in short bursts. It's plenty powerful to take out all but the most powerful enemies. Doing this will keep you from being exposed while recharging the laser, and take down more enemies faster.

Run Mission 5 on easy, and take your time to preserve the mech's health. Once you get to the section where you have the scrolling platforms, the mech will be teleported to the opposite side, leaving you to negotiate this area with out it. Once you reach the other side, you will get it back. The last section before the run up to the boss requires you to be precise in your movements to avoid the lasers.

Once you get to the boss section, use your lasers to quickly take out the turret-things at the top of the room, being sure to clear out the enemies that spawn in immediately. In the 2nd phase (wall shooting at you) - stay near the back (left) of the room and use laser on full blast.
For the final phase (skeleton-acid-worm-thing), just pay attention to his patterns (he telegraphs each of its next moves) and focus on avoiding the acid droplets that drop off him as he does his arcing leap over you. Immediately shoot down the flying enemies that appear from left or right upper area. This will repeat several times, and just focus the laser on the boss as he jumps over you and vertically under you (look for the telegraphed acid wave below, and side step it).

The mech is found on mission V in the second section, the mech controls are as follows:
Movement is as normal with the joystick
is to jump
is to jump out of the suit
is to attack
Fires a homing missile
Fires a particle beam

This is by far the hardest mech achievement to obtain, playing on easy makes this doable though. I make a few mistakes while playing and can surely be improved upon.