I kinda regretted ranking up my 5* knull, I even gave him >100 sigs. I was all in on the hype then, saw several videos from youtubers and their r3/r4 knull. I took him up immediately without even testing. In the end, I was a bit disappointed with his dmg + he needed to be ramped up in every fight. His regen wasn't as great as I expected either. (I don't run suicides, I anticipated him to be worse without it, but not to that extent). However, with the addition of bg, he's been a decent defender for me. So, I regret it a bit less now...
Silver centurion
Going to get a lot of flak for this, but R3 doom. He has gotten extremely boring and I prefer using other mystics over him.
This guy ... literally sucks ...i ranked him up for BG attack and he couldn't do s**t over there too ... was so excited when i pulled him but it ended up being my most regretful rankup.