Here is my 100% Achievement guide and full walkthrough so you don't miss a thing.
This is unmissable.
In level 2, you learn how to use your holoblob.
This is done by pressing and holding the
button on a human.
When the disguise starts to run out, make sure to find another human and again, press
on him or her to keep your disguise going.
A quick note, dont use the holoblob unless your hidden.. if someone sees you, the police are alerted and you have to run or gun.
Go to 17:20 in my part 1 video to see where and how to unlock this
Hope this helps!