Drown 5 Enemies in Oil during Combat
It is recommended you use an oxygen suit for this area (obtained as a side quest automatically triggered when entering any anti-oxygen area).
To start off, you need to find a location that has both enemies and tar. Choicest options for these are the Deadzone (at the southwestern edge of the map) and the Kluppy Dunes (in the northernmost portion of the map).
Look for the bandit-type enemies (same as the size of your character) and bait them towards the tar; only to use the knockback on your melee to push them into it completely. Additionally, an easier method to getting this achievement is by acquiring the Mucus Bubble ability (listed under Biogenetics) which lets you roll over enemies.