Why abandon the chess motif at the last moment? You had something good there and then you went cliche.

How about:
Rooks, super strong and resilient
Knights, fast and agile, capable of running as fast as a horse, masters of the blade
Bishop: Capable of firing creating an energy shield to protect themselves or others and healing
The Queen: The Sorceress, capable of hurling elemental bolts but can't make shields
The King: Can summon ten shadowy warriors, also can command mortals and even one chessman but has to concentrate completely on the chessman