Mark Blaine, a.k.a. Chillblaine, first made his presence felt in The Flash‘s seventh season when he became a potential love interest for Killer Frost. Arrogant, good-looking, and charming, he clearly had chemistry with the Team Flash hero, but that’s about it.
The show did very little to make Mark a strong character beyond his relationship with Frost and it was only when she died that he started to grow as a character. That is, until season 9 made him betray Team Flash and wanted audiences to believe he was a hero who deserved to be saved when he did very little to suggest that was the case.
I personally didn’t have that big of a problem with Chillblaine until season 9, but it’s easy to see where the fans were coming from. A relatively two-dimensional character that was fun from time-to-time, it was nice to see him get a little depth in the back half of season 8, but that wasn’t enough to justify making him a main character in a final season already overstuffed with meaningless characters. And the way he has acted throughout the Arrowverse’s final season has not justified that decision.
He was fine in small doses, but like with everything The Flash has done post-season 6, he was just another missed opportunity.