A 4312 I have mostly tested on Portsmouth.
I was bored of using 4231's so I thought I would give a go making my own formation.

The formation is supposed to work quite attacking - high pressing lines, high attacking lines.
With the wing backs I have them on support to try and whip in those FM22 crosses into the box as best as possible, with high-crossing-attribute wing backs.
The midfield consists of a Mezzala on attack who makes those runs into the box to supply the attackers but also take a few goals of their own.
The formation mainly utilises the midfield seeing most of the goals come from the midfield due to the attacking mezzala.
The attack consists of a shadow striker, a false 9 and an advanced forward to fully utilise all areas of the attack. The AF does spend a lot of time out wide to get crosses in to the F9 and the SS but the pace of the AF is also used on a high pressing counter.