Here's how I would envision Megaman X placed into SSB:Brawl.
B: Charging buster cannon attack. Fires one enourmous blast when fully charged. Low damage, high knockback.
Side+B: Fires a random projectile from the Megaman X series.
Up+B: Megaman-style teleport.
Down+B: Turn into Zero.
FS: Calls one of the X-series power armors.
B: Charging buster cannon attack. Fires multiple big blasts when fully charged. High damage, low knockback.
Side+B: Attacks with Beam Sword plus Beam Sword beam. High damage, high knockback, the beam moves somewhat slowly compared to other projectiles, cancels out all other projectiles it touches.
Up+B: Does a rising slash with his beam sword.
Down+B: Turn back into X.
FS: Repeatedly slashes the nearest opponent (similar to Link's FS)