Much of the video game industry is just companies/devs copying each other (but of course, due to a lack of freedoms, each company either uses proprietary game engines or badly reimplements things).

Fortnite Battle Royale is just a copy of the same concepts as PUBG. No one really gives a shit as no one has earnestly tried to patent general game design concepts.

So yeah, go crazy as long as you don't violate trademarks/copyright. As a personal note, please try to make your game libre. It might actually help you if someone accuses you of copyright infringement and it will also open an avenue of distribution into libre operating systems which can increase the longevity of your game (look at things like 0AD and Supertuxkart) instead of competing for mindshare on sites like Steam, Gamejolt or itch io.

If Palworld is anything to go by, you can get away with a lot. And I think all the mechanics and broad strokes thematic elements are fine to yoink fully, Path of Exile took the shape of the UI and control system from Diablo II pretty much untouched (of course, details change, but the look and feel are extremely similar). The building system is nothing unique, it's just a global grid based system where you can place walls, roofs that double as floors, ramps, and edit them to add doors, windows, and cutouts. Satisfactory has a similar building system (albeit not on a global grid and without the editing function), and the rest of the game is so dissimilar you wouldn't even think of comparing them.

As long as it's a legally distinct product (no confusing trademarks or whatever) and you don't literally rip assets, or decomp code and re-use that, you're good.

I think you're really fine here for taking most of this. Orcs Must Die and its sequels are all relatively like F:STW and I didn't see anyone draw any parallels between the two from even a casual "gee these sure share a lot of similarities" perspective. Granted it's been a while since I've played Orcs Must Die, but from what I've seen from STW they definitely seem to share a lot of ideas between them.

So long as you aren't taking some patented system (like the Nemesis system from Shadow of Mordor) I really think you can basically make an exact mechanical clone without any legal team really biting. In Epic's specific case look at their acquisition of Fall Guys and the popularity of something like Stumble Guys and the lack of legal action there.

I've been working on my Advanced Wars clone for a while now, and so I've researched this a little bit. Game mechanics almost basically can't be copyrighted. It also helps (in my case) that I'm not really cloning 1:1 as much as I'm making a substantially different game in many key ways. Also I'm not using a sprite sheet found online, I'm making all my art assets myself at slightly higher resolutions. Mostly you should worry about:

• using assets (art, sound, other files) you don't have the rights to.
• using trademarks you don't have the rights to.