I have paired B2 with Phasma and am having good success. B2 attacks so often it just makes sense to try and trigger a bonus attack.
B2's Mow Down is preventing any one from casting a taunt and if it is cast it is very shortly dispelled. (I am really thinking teams will need counter B2 with a dispel effect such to allow fr taunt).
My immediate team is Phasma, RG, B2 and the IG's. (I do not have Rey and when I get QCJ maxed he will replace IG 86).
For those with Rey wanting to use B2 consider Phasma, Rey, IG88, RG, B2.
I could see a better composition with Phasma, Echo, Rey, B2 and RG. Echo will proc off of B2s many attacks.
Finally there is a case to be made to remove RG but I have not tweaked that just yet.