If you have 1000+ N-keys you get pink cases/key 100/0.
It is good to save up for pink keys in other events.
Unused keys from 3th gambit are given back to players when 4th event start.
First half of 3th gambit was bugged non of my 100 friend got the SR-Girl in first half of the event.
This mistake was fixed and the SR-girl was easy to get in 2nd half of 3rd gambit.

In this event the chance of the SR-Girl is around 1 in 15 when using silver keys as is intended.

4th Gambit dont seems to be buged so it is better than 3rd imo.