User blog comment:RoznosicielCiast/Least popular champions/@comment-4593717-20130130174045

I play all of these champs except Heimer, Karma, and Viktor. I see no reason for any of them to be underplayed... OH WAIT YES I DO.

They have niche roles (excluding Sion, Viktor, and Xerath) and therefore don't fit into teams well.

The reason why people might not play Sion, Viktor, and Xerath is just that their kit is a tad clunky. Sion for example has annoying AA animation. Viktor's primary spell, Death Ray, has an extremely high skill floor. Xerath's Locus of Power takes too long to come in and out of, and he has almost no way to kill someone without his ultimate being off of cooldown.