To be fair, he wasn't exactly the main focus of the ep. I know there were people who were excited about this guy, but I wasn't. I first looked at his design and went, "Eh, I dunno, I'll let him play his part judge him later." He didn't get a lot of screen time, but people should've seen that his horn flew away fully intact. He'll be back.
And also, unlike the other villains, this guy thought ahead. Where else would that pressure alarm have come from? And for that matter, what would've stopped him from countering the spells of two very powerful unicorns? He didn't count on Spike of all people to save the day, but still. He's not exactly stupid.