Space Otter Charlie

I got this by replaying the final mission and landing on the buildings on the asteroids with the mech suit and pressing X to melee kill them. I kept suiciding and doing 4 of them in the 1st area until I thought I had done 30 and it didnt pop. But once I entered the next area and melee'd a couple more it popped.

You can also use the upgrades slide ability to slide into the pillbug looking foes on curved surfaces.