Copyright issue for the development of a similar clone game

Question

Copyright

Good afternoon. I recently remembered one game that was popular on the j2me platform 10 years ago.
Until now, there are either no analogues for iOS / Android, or they do not repeat the original idea too much.
And recently, the developer of the original game tried to make a port for Android, but in general everything changed in the game, it became ugly and uncomfortable.
I tried to implement all this, I was able, it remains only to complete the levels.
And now the main question. If I want to sell this game, how do I deal with copyright?
Differences:
1. The name of the game will be different
2. The ability to choose the appearance, in one choice there will be 1 in 1 colors, as in the original game.
3. Different level selection menu
4. I have more thoughtful physics
And it’s also interesting how dozens of analogues of Angry Birds / Flappy Bird coexist so peacefully, because in some games they just changed the bird and that’s it, is there really no copyright infringement here?

Answer 1

First, it would be nice to find information about what rights are assigned to the author.
Secondly, you need to get rid of the similarity of content (images, sounds and videos). It is highly likely that the content was prepared not by the developer himself, but by employees. Accordingly, the author may have documents transferring rights to this content. This moment the author can use to sue you.
Thirdly, making clone games (namely clones, not similar ones) is a bad thing to do. Clone games are badly treated by players, the authors of the original. There are few benefits, but the reputation will be tarnished.

Answer 2

"I do not create, I only repeat what I have learned" (c) Confucius

Answer 3

All my life I thought that repeating ideas completely is bad and you can regret it, but looking at the number of various clones of Angry Birds, Subway Serfer and Flappy Bird, I understand that if you change the drawings leaving exactly the same shell, everyone will spit.
And so, it is really worth knowing what rights the author has.