Nostalrius Begins - Quality wow vanilla realm (1.12)

The release is close, I heard there were PvE tests of some raids, those who participated can you share your experience? What instances, bosses, any bugs on them? Did class mechanics work properly?

Onyxia: Fear was bugged at first, got hotfixed. Everything else on her works perfectly
Molten Core: Luci / Gehennas / Magmadar work perfectly. Another guild said garr adds were bugged but it wasn't for us, probably was hotfixed. Didn't get any further.
Kazzak: Works perfectly
Azuregos: Works perfectly

Class mechanics: Seem to be working just fine

What about the true end boss of WoW?

The Cleaner.