The question is a bit flawed. Doing art like this it's really only 'hard' to attempt to push the envelope beyond your current comprehension of the subject.
For an artist already skilled enough to make it, it just comes down to having the proper motivation or willpower to commit the time needed for completing the project.
But it's not really 'hard' as in there being any sort of difficulty involved in actually performing at the level you've already reached.
If by 'hard' you mean "how many thousand hours will I have to practice before I can be expected to make something similar to this" it'll of course wary from person to person.
People learn different tasks at different rates, but expect it to be a process that will take at least a few years of serious studies if you're just starting from scratch.