You can pick up the
Disappearing Ink with Bernard (
kid with glasses in the present).
From the main lobby, where you start the game, go upstairs (
on the right). Once upstairs, go to the middle room (
it has an "R" on it).
you should see the
Disappearing Ink on the small table next to the door. Pick it up.
Now, when you have an opportunity, use the Disappearing Ink on anyone you see. I was able to get this with:
Dead Cousin Ted - Just outside the manor. From the main lobby, open the front door. Ted is the mummy holding the birdbath. Be sure to talk to him as well for Bernard's part of the achievement "
Are You A Mummy?".
Guy wearing Ski Mask - From Dead Cousin Ted, go right until you see the guy with the ski mask trying to break into a car.
Portly salesman- From the main lobby that you start the game in, open/go through the double doors with the WELCOME sign above them. Go to the right of this room to see the salesman.
Sleeping guy - From the main lobby that you start the game in, go upstairs (
on the right). Once upstairs, open/go through the first door you see (
it should have a "W" on it). You will see a large gentleman sleeping on a bed with a heart-shaped headboard. Close the door to this room for another achievement if you haven't already.
Green tentacle - Exit the room with the sleeping guy, go to the right to the next door (
has an "R" on it). You should see the Green tentacle in the middle of the room.
If you see a way to improve this guide or want further clarification, leave a comment! Thanks!