Azura is really strong (she is blue, with lance). I don't know how she'll hold up against Robin, but everyone seems to hold her in high regards.
as a Robin user the nastiest surprise I've had so far was actually an Abel. I use my own Camilla to deal with enemy Robins. Also yeah, that team is the definition of Robin fodder.
I try to take him down with Camilla.
Robin is surprisingly tanky. I find that if I lose Camilla before hitting Robin with her, Robin will likely wipe my team.
Yeah, don't have any of those units. I'd have loved to have gotten a Camilla, but alas all I got from that banner were the pair of Takumis. I'll keep an eye out for when I'm summoning.
I do have my own Robin. Only 4 stars, but I'm doing well enough in the arena that I might be able to upgrade him to 5 later on. Also a 4 star Kagero, who I'm seeing a fair bit up hype for. I have so few green units though, it's exasperating some times.