Bionic Commando

For the achievement, simply kill 15 Biomechs over the course of the campaign. You will definitely kill 15 as long as you kill all of the ones you encounter, regardless of the difficulty setting.

There are different types of biomechs, and the game doesn't explain how to deal with enemies so I'll explain some here.

Basically, all Biomechs have a vulnerability on their backside, which looks like a glowing circle that gets highlighted red by your Bionic Arm reticle. It's on their upper backs, between their shoulders.

What you need to do is either take them out with high power weapons (like the Bulldog, Grenades, Tarantula), snipe their backside from a distance (the game gives you one or two opportunities to do this while you have the sniper rifle), or take them out with hand to hand combat.

If you're going to use a gun, just know that it will probably be depleted on one or one and a half biomechs. Make your aim count.

The first biomechs you encounter are shield biomechs. They carry a shield that they plant down on the ground and it begins to glow blue around its edges. When they do this, it allows you a brief moment to try to quickly get behind them to latch on with your bionic arm and follow up with a zip kick.

The next type don't have shields, and are more aggressive. They use their wrist shotgun more often, and jump towards you doing an overhead axe maneuver. When they attempt that, dodge as when they land without connecting with that move, they pause for a moment, allowing you to get behind them and zip kick them.

Another type of biomech is the welder biomech, that carries a long tube-like weapon that shoots a constant blue stream of energy (like a laser). At these points in the game, you can knock the weapon out of their hands and use it freely against them and any other enemies. Note that while holding the weapon, Spencer's maneuverability is greatly handicapped.

One pain in the ass type of biomech is the flying "hadouken" biomech, which tries to shoot a ball of electricity towards you, after hovering in the air and posing the way Ryu from Street Fighter woud, when launching a "Hadouken". The trick with them is to shoot their ball of energy while they're charging it up, and it blows up in their face. You can then follow up with your arm and zip kick to their back.

Stay away from Biomechs, and always keep moving and swinging (if you can swing), as they do HEAVY damage if they grab you (which they tend to do up close).

One final note: when you get adrenaline, if you have it maxed out and grapple a biomech from behind, you can use the adrenaline attack (y + b) instead of zip kicking to perform a one-hit kill on them.

Good luck!

OK biomechs come in pairs almost every encounter and until you get the adrenaline ability you may have some trouble fighting both at once especially on the high difficulty settings. So the key is to only fight one at a time from elevated positions so you can use death from above and then as they stand back up keep using the grappling kick. grenades are also very helpful as well as the bulldog. With the shield mechs its really easy to maneuver around behind them and get the kick off. With Beserkers and the laser mech you have to use the death from above and only fight one at a time whenever possible.