Pretty sure he just comes in for Robin's final smash, and attacks with Robin. I don't believe we've seen Lucina's.What's the the deal with Chrom? Is he AI-controlled or does he replace Lucina for a few seconds?
Also, RE: Fire Emblem Awakening. Robin is the player's character correct? So they'd get priority over everyone else; maybe 95% of the time (maybe next time Pokemon Trainer).