Gatling Gears

*This achievement can be done in single-player or co-op, however this guide is for doing the achievement solo.

Solo Method:

I personally believe the easiest level to get this achievement on is Katharsis - Terminal (Chapter 5-1).

Play the level a few times and try to get familiar with it. You'll want to be sure to watch for the little floating electric bombs that come out in the level every so often. They are hard to see and can hit you very quickly if you don't know where they spawn. Make sure to learn the areas where these little floating electric bombs spawn as to take them out quickly. Their spawns in the level stay the same every time, so make a mental note of where they appear.

I personally would wait for the very end of the level to use your Spark Bomb. Wait until you get into the square arena at the end and clear a few enemies. Wait for the little floating electric bombs to spawn and then immediately hit your spark bomb. This should clear every enemy off the screen and then spawn the final tank. Take care to not get to close because the tank's machine gun can hit you at close range. Stay far enough away and launch grenades and missles and the tank should go down in no time.

Difficulty does not effect the achievement. I would suggest playing on easy. Use grenades and missles wisely and make sure to be fully-leveled up, to make killing enemies easier, if not using the Mega Walker.

When I went for this achievement I did not have the Mega Walker unlocked (To unlock the Mega Walker you need to have at least 300 unlock points in the Unlockables Section, so a play-through of the game will be needed to get these points). I used the traditional, fully-powered up mech, but after unlocking the Mega Walker it seems that it could possibly be more powerful. Experiment around and see if it helps using the Mega Walker.

Katharsis - Terminal (Chapter 5-1) as Otis dRiftwood stated in the above guide is by far the best choice. The only things to make sure you do is 1). CO-OP all the WAY! I got this achievement the first try with a co-op parter. You hang back and let your parter take the lead and take any stray bullets flying your way! 2). Use the Mega Walker! It has stronger weapons all around. 3). Move VERY SLOWLY! I mean Crawling in some spots because of the Large amount of enemies on screen is a few key areas. If you inch up little by little you can pick them off in much smaller groups. 4). Both you and your partner save your Spark Bomb for the Last area. Use one fairly soon to clear out most enemies and the second after the last enemies come on the screen.
Super Easy!

The other guides here suggest doing this achievement on Chapter 5-1, but after a few unsuccessful attempts I tried chapter 5-2 and got it in one try. There are a lot less nasty surprises and most large fights are preceded by a powerup spawn.

The advice remains the same: inch forward until you can see the tips of enemies at the edge of the screen and use your rockets and grenades to shoot them until they're fully spawned. Take your time, if things get hectic, concentrate on staying safe and be careful not to get backed into a corner. Do not attempt this unless your walker is fully upgraded (or better yet, use the Mega Walker.)

Try to leave your spark bomb until the end of the level which has 2 giant tanks, 2 flying gunships and then a final giant tank. You'll find a grenade booster spawns just before this fight, so here's how to do it:

- Pick up the grenade booster and destory the first two tanks (the grenade booster will actually remove enemy bullets from the air)
- Once both gunships are on the screen, destroy them with your spark bomb (Y button)
- Use your rockets and grenade to take out the final tank. He shoots a stream of bullets at you, so don't move around too much, else you'll widen his firing arc and it'll be harder to dodge them. EDIT: I found on my hard playthrough that if you're able to hold out long enough, it's possible to hit the two gunships and the last tank with one spark bomb, but at increased risk of getting hit.

Good luck and if you get hit, don't get frustrated - continue to the end of the level and then restart, that way you'll learn the layout of the whole level.