First off, if you get nauscious, you are doing too high a dose at one shot. You can spread your injections throughout the day. Antibodies will build up in your body, and too high dosage will trigger some defenses, so dont go too high on dosage. If you tan extremely quickly, extremely much, then you are also running too high dosage. You are better off running it too low and adjust with solarium, than to inject a lot and get black. First time I used it, I got so dark I got attention from everyone and everything around me. I am going easy on the dosages now and I am used to it, so I know when to stop, etc.
I have never experienced a drop in libido after using it for a while.
Moles tend to get darker, as they would if you were tanning normally. Freckles will get darker and sometimes there will be "invisible" frackles that will become visible. After a times use, this will smooth out.
As for scaring etc, you should never tan your scars, they will become permanent. Same thing goes for melanotan-2, you should follow the exact same skincare rules as you do while out in the sun.
The reason why I like to use a solarium is that I use half the loading and can begin maintainance quicker, saving a few bucks. It is not unlikely that you will get a feeling of being pale, even tho you are incredibly tanned. I keep feeling pale even tho I know im more tanned than anyone else.
I think another side that most will appreciate is the weightloss. I shed fat weight while on MT-2. I also feel euphoric and happy, satisfied. To me its great stuff. Maybe not for everyone, you have to be patient and carefull, dont overdo it or try to rush into color.