Havok is pretty interesting. I always really liked the character in the X-Men comics, and I think he has one of the coolest costumes of all time - which we’ll never, ever see on screen. Still, that thing on his chest is sort of like it…. just way more complicated, as movies will always do.
And finally: The Beast. I really love his featurette, and I’m intrigued by the idea that he’s in a romance with Mystique. X-Men lore is thick and confusing, but off the top of my head this seems to be a new addition to the mythology (although there was a point where they tried to intermingle all the blue characters, so who knows). I imagine poor Beast is going to get really upset when the red demon dude makes off with the girl (not a spoiler because I haven’t seen the film, read the script, but Mystique and the red dude are Nightcrawler’s parents). Fitting for poor Hank McCoy.