Watch out with fanmade games. They're more often than not grimderp shit, with painfully obvious modder issues and EDGE!!! permeating everything (Pokemon Reborn being one literally bloated with that and too much content and a long development time nearly equal to Dworf Fortress). Some are allegedly good, such as one whose name escapes me that had you use Pokés as a party, has custom forms of known Pokemon and even C&C. IT starts in a new region and Hoohoo is featured in the "cover".
All around a pleasant experience, though again, only the optional stuff can be considered challenging, at least based on what I remember
Sun&Moon are quite good, Mega-forms are not available until post-game, even random trainers have access to super moves and you can (and will) be trashed if you don't have a competent team by the Elite Four. The plot is shit and tries too many things at once though.
Supposedly Ultra-moon/sun improves the gameplay, makes it even more challenging and has a less inane plot.