Hidden Phantom, stealth expert and commander of the Cutting Shadow Squadron. Later as Model P, he was biomatched to Siarnaq (second image). Third image is his Biometal form. He is characterised by his calm but ruthless demeanour.

Phantom is also unfortunate to be killed in the first Zero game, thus sitting out the second. He returns in Cyber-elf form in the third for an optional battle, though, and joins X in support of Zero by the end.

Phantom, unlike the other Guardians, does not have a Robot Master predecessor in MM9. He does, however, greatly resemble Shadow Man from MM3. This is unusual. Unlike these later RMs, Shadow Man has an ambiguous otherworldly origin, unknown as he was reprogrammed by Dr Wily. It is plausible though that he could have been reactivated by Light later and studied, thus informing some of his later designs. Phantom always seemed mysterious to me as well, possibly as a result of his powers. Regardless, the two definitely share design characteristics, based on Japanese ninja archetypes.

The fifth image shows the Shadow Armor from X6, perhaps the most direct Armor relation with its ninja motif and stealthy powers.

As for the Copy Abilities Phantom embodies, the most fitting are Dark, Cutter (shurikens and whatnot), and Time/Space (what with his teleporting and illusions).