Help with developing ground styles (Ori, Hollow Knight, SpriteShape, etc)

Greetings all, a new poster to the forums here. I have been using Unity for a month, diving head in to several Udemy courses with inspiration to design my own indie game, so forgive my lack of experience. One important aspect for me is an immersive environment. I look to Ori and Hollow Knight when I think of projects with unique and immersive art styles. The part I am lost in is how some of the grounding was set up in these games. I am hoping my questions below can be answered so I can have create a more defined direction in designing my game. Thanks for your time.

Ori: I understand the sprites were created in 3dmax, and converted into 2d sprites. Was the same done for pieces of the environment, or was it hand painted? How is the character colliding and walking on this environment? Is there a hidden tileset like in Hollow Knight? Is it just a single hand drawn line (I don't even know if that is possible)?

Hollow Knight: From my understanding, there is a hidden "black tile" map between all of the layers of a hand drawn environment. I have seen the gif of their multilayered system. To get these multilayers, did they just give different sprites varying z-positions?

Sprite Shape: This is such a great asset addition to unity, but I am having trouble with corners working properly (they don't show up). I am following Unity's youtube tutorial series completely, yet I have this one hiccup. Has anyone else experienced this, and if so, how did you resolve it?

 

From what i see, Ori is a 2.5D game, meaning those are actual 3D objects with 2D colliders attached to it.

You can create Edge colliders and polygon colliders to easily "Hand draw" a collider. If you need curved colliders, check this : https://stackoverflow.com/questions/25958171/how-can-i-create-a-2d-curve-collider

Hollow Knight might use a technique called parallax (not sure tho, i can't access youtube right now and check).

I didn't try Sprite Shape yet, can't help you with that.

 

From my understanding, this tile map is used to try and validate the level design by gameplay iteration before actually "dress the level", I suppose it stays then as a simple polygon collider for physics and collision.

The parallax is indeed working with simply different z position and a non-orthographic camera.

I haven't used it for a while because of this reason, if you manage to make it work properly please, let us know !