This guide is to help you get the Specimen GG achievement. I wrote this because I saw no other guide for it.
When you start the chapter place 3 satchel charges where the crystal stations are.
Like so: If you place 4 satchels per crystal they start to blow up because there is a limit to how many satchels you can have placed at one time. So the number of the satchels placed shall be 3 (2 is not the number that thou shalt throw unless thou then proceed to three, for it is not enough) (FIVE is RIGHT. OUT.) You can get more satchels since you can't carry all 9 at once.Then play the level like normal. When the floating baby bastard brings up his crystals to heal, detonate the satchels and then you should get the achievement. The satchels might get blown away by the Nihilanth's or tossed away when the crystal rises, so its best to save when you finish placing all the charges and/or right before the crystals are brought up.