Difficulty any (Heroic/Legendary not required)
Skulls) not required
"after finding CPT. keye's, look straight to the floor and then a little to the right, you'll see a ten tentacle, going over the edge follow it and look directly at it, shoot it if ya want "
and that should be the achievement, if you have any issue like achievement not poping try and shoot it or check to see if it's non-poped but unlocked