Youtube RLFM Just2Good has just released their review for the LEGO Collectible Minifigures Series 18 and we are getting the box distribution of the series which is reproduced in the graphic below.
4 in a box
Brick Costume Guy
Martial Arts Boy
Peapod Costume Girl
5 in a box
This series was scheduled for a May 2020 release but it looks probable that we might potentially see a April release now.
*A review by Brothers Brick shows the same distribution for their box.
*Note that not all box distributions are exactly the same and there may be some small variations from box to box.