Someone pointed in event page in response to my math wall of text that the random RNG chest in Ultimate map is a normal chest aka one that drops (for me at least) only 2* girls, not dumplings. I run that map few times and actually got that chest each time so can someone else confirm that? I rather run Advanced map for a bit more exp as with my 6* and 5* drop luck I will probably have enough crystals from daily quests alone XD (a.k.a. my only reliable source of 5* are events and reissues). (EDIT - checked it myself it is not dumpling dropping chest, neither it is life crystals one - so static 0.5 ratio for dumplings and no RNG there, no RNG for crystals, only RNG for that chest that drops a 2* girl most of the time /EDIT).

If its true I will need to edit few of my posts to remove misinformation from them.

Also in last event at least in Advanced map (which dropped 2 crystals), I got once or twice a 3rd crystal. Not sure if 2 bonus ones mentioned in few posts above is wrong, or is it 1 or 2 and I was unlucky in luck of getting bonus ones, or is it about this event (didn't get lucky yet in this to get more than basic 2/5).