After some googling, the Mori Mori Rush looks to just be a upgraded weekly weekend gold event that replaced the old one. Basically a 4th difficulty stage version.

https://goo.gl/IVNES6

Need confirmation though cause I clearly don't know as I've been playing for less than a week.

Quote Originally Posted by nazrin992 View Post
RNG Chests in maps I presume as the wiki said. Like, Manyuu dailies or Dragon dailies or even the SG Manyuu or Amphys in stage 12 and above. Most will have a chance of obtaining Golds and this one is no different.
Ah, that means more spamming runs. Meh, I just almost finished the previous event too. Haven't been able to focus on leveling in a while and at this rate, it doesn't look like I will be.