> Tuff including all graphics, characters, ideas, sounds and maps are Copyright (c) 2014 Ivo Wetzel. All rights reserved.
(emphasis mine) IANAL, but my understanding is that at least in the US, it is the expression of the idea (the software and code, the graphics, and the other things mentioned on that line) that are subject to copyright, not the idea. See https://en.wikipedia.org/wiki/Idea-expression_divide.
IANAL, and yes, you can not copyright game mechanics or ideas. This is why so many clones of every game exists. Because no one owns the rights to "a tower defense".
There is only one successful Tetris clone lawsuit.[1] Most Tetris clones are removed just because they are fairly aggressive with their claims (not necessarily because their claims are valid).
The successful suit was due to the playing field having the exact same dimensions as well as very similar visual expressions as regular Tetris outside of the just the game mechanic.
(emphasis mine) IANAL, but my understanding is that at least in the US, it is the expression of the idea (the software and code, the graphics, and the other things mentioned on that line) that are subject to copyright, not the idea. See https://en.wikipedia.org/wiki/Idea-expression_divide.