I believe you can’t have a patent / copyright on a context / idea. If you are not actually copying any of the source code itself but actually create something similar from scratch, you should be on clear waters. For example Apple Store is filled with games that are basically copies of each other, only graphics, general quality and flow of gameplay varies a bit and no lawsuits are being thrown around as long as actual copying is not being done. However if you mimic the original down to minute details it will cause bad blood and make your work feel “tainted”, so it should be always your goal to actually improve / make your own twist on the work you are inspired on.
Of course you should contact Envato and ask their official take on where they draw the line, because marketplaces can have their own limits.