Where can the combined Bishop/Pawn (Biawn) on b2 move?

Solution: The Biawn can move as the Bishop or the Pawn.

Biawn moves forward as the Pawn to b4.

The notation for this is: BPb4

OR,

the Biawn can split, and the Pawn or the Bishop can move away.

Here the Bishop splits and moves to e4 leaving the Pawn behind. (notation Be5)