"Awarded upon completion of episode 4."

It's as simple as that.

"Talked with everyone in the apartment in episode four."

While walking through Addison Apartments with Larry, check in and speak with every resident.

"Where did these come from?"

Collect all teeth from inside the apartments. The locations of the teeth are...

N Tooth - On the basement level, in the apartment that isn't Larry's, go into bedroom #1 and go all the way to the left.
E Tooth - Room 102, to the right of the door.
Brown Tooth - Room 202, in the bathroom on top of the toilet.
S Tooth - Room 304, on the kitchen counter.
W Tooth - Room 501, after the creepy hobo scene, walk all the way to the left.

"Never failed any of the barrier songs."

While blasting through chunks of the sword with your guitar, don't make a mistake on any of the songs. I believe this one is glitched since as long as you make it through all of them, you will still be awarded the achievement, however, this may have been fixed in an update.

"Collected all VHS tapes."

There are 9 tapes to collect throughout the entire game. Here are the locations...

- Lost Unlock door 4 during the prologue. The code from top to bottom is: diamond with box in middle, rectangle with v shapes cut into top and bottom, then the diamond with the upside down Y shape over it. The tape will be in the VCR after you talk to Edgar and go through door 6.
- Phantom In the back of the shed, code is: 4035364
- Others In Packerton's room, in bedroom #1 there is a patch of ripped up carpet, use the pocketknife and then enter the code 435542
- Bridge Room 404, use the pocket knife on the broken tape
- Hunger Room 503, hidden in the broken wall
- Skin As Larry, enter room 501, press R around the hobo. As Sally, enter room 501, grab the key where the hobo used to be. Room 504 will become unlocked. As Larry, enter 504, go through the hole, and press R around the tape. Sally will now be able to pick up the tape in the hole.
- Evolve As Larry, enter room 404 and walk to the back, press R around the tape. Sally will be able to pick up the tape in room 404.
- Rage While Larry, place the pony from room 303 on the pentagram on Charley's floor. Sally will be able to find a tape where the pony was
- /// [DO NOT SEND LARRY OR SALLY IN ROOM 103] As Sally, enter room 104 and grab the carrot, place it in front of Gibson's door cracked open. As Larry, grab the lighter from where room 104 should be and light the rabbit in front of Gibson's door on fire then press R.

"Had all optional conversations with Larry in episode four."

This achievement is awarded upon having all optional conversations with Larry. As far as my personal experience went with getting this achievement, it has nothing to do with the conversations about the teeth or the tapes, since I was awarded this achievement with only 4 teeth and 2 tapes. It is only concerned with the optional or extra conversations, which are not related to progression of the storyline or other achievements.

- Make sure you interact with all people and items at least twice and for some items, three times. For example, the noose in room 504 requires three separate interactions as it gives three different texts.
- Make sure you visit all areas of the apartments, including going out to the treehouse.
- Make sure you revisit certain areas, for example, when you first meet up with Larry and are in that walking sequence, walk out of the section with the house and then walk back to it. I walked back to the front door and interacted with it, and started to walk away again, this gave me a new conversation with Larry that you wouldn't normally get.

"Destroyed The Endless One without falling."

During the final boss battle, don't mess up any of the songs so you won't fall towards the bottom.