Did the mountain alone. Got by mini-bus to Koto Baru from Bukittinggi and up I headed. My trip happened to coincide with a public Indonesian holiday, so the trail was full of people. It was also raining heavily throughout the whole first day. Camped just before the end of the forest, at ca 2300 amsl, and went then up to the crater by sunrise. Very unique, extraterrestrial-like, landscape and great views. Saw some rare Leontopodia (edelweiss) some way down towards the east slope.

Full report:
http://dimitriosfan.com/2016/06/28/mount-merapi-on-top-of-an-active-volcano/