...How is an Incredibox mod supposed to be difficult? It's a musical/visual sandbox. Well, that video recommended I should try it myself before watching, so I'll give it a go, despite not having previously used Incredibox. I have seen several videos, so I know the general deal.
Alright, reporting in after getting all achievements, the "difficulty" only comes from two sources. One is the chaser, appears occasionally and follows your mouse, if he touches your mouse, you lose. He goes away after a while. The other is the crasher, taking the place of one of the...guys you can place, whatever they're called. Don't use him, or you lose. Would be easy, if not for the occasional swapping of two of your instruments, combined with the icons for them being blocked much of the time by an eye graphic that replaces them. Your goal is just to survive while still occasionally adding or removing an instrument, the time stops counting up if you don't do one of those things for 4 loops, the loop time being indicated by a wheel.
So, I wouldn't exactly call this difficult. Not at all, it's pretty easy. The crasher is seldom actually targeted by a swap unless you are exceptionally unlucky, and the chaser is just a matter of...moving your mouse constantly until he goes away. The most demanding achievement just requires you to keep the mix timer going up for 6 minutes, which isn't that hard. (If you idle for too long, the timer only pauses until you act again, it doesn't reset, if anyone's worried about that...you probably already know that if you're reading this, though.) The only thing that actually adds difficulty is trying to keep a good sounding, dynamically changing mix going...but then the icons being hidden and the chaser physically stopping you from really using tools like the headphones to isolate the track to just one instrument at the right time to pull off the really good stuff, so at some point you resign yourself to just randomly swapping guys in and out and accept the result while endlessly dodging the chaser. Keep track of where the crasher is, occasionally remove a guy then fill his slot with someone else some seconds later, and you win.
Credit where it's due, the time did pass quickly for that 6 minute mix. A lot of the instruments here are nice, it's a high quality Incredibox package. Getting all achievements unlocks "Mercy" mode, which I'm pretty sure just disables the mechanics so you can play with the instruments the normal way. Crasher still crashes you, though, he has no mercy. Fun fact, I noticed after a while that the buttons on the guys scramble themselves every time you mouse over them, thought I was just being sloppy when I kept clicking something else when trying to click the headphones to isolate the instrument.
Overall, pretty alright, but the claim that it's made to be "difficult" is overblown, it's just a pretty simple survival and endurance challenge, so don't be intimidated by it. Reminds me of old flash games, a simple challenge with accompanying art and music that lasts you 10 minutes, and that's not a bad thing at all. That format allows for a lot of creative expression, and this is pretty well made, on that end.