I'll go with these 4.

• I really liked Missouri. I can't say I loved her cause she wasn't on the show enough for me to feel like that but I would've really enjoyed to see more of her. Especially in the first seasons, I could see her establish a pretty good dynamic with Sam, helping him understand his psychic powers more. I think she could've been a really good parental figure to both of them. And she cracked me up sm so why not lol.

• Henriksen was probably one of the characters that had the most potential imo. He was interesting, he stood his ground and he could've done so much more. I always thought that it would've been cool for them to have someone like him as a friend, to help them with the law. They really wasted his character.

• Where do I even start with Kevin. He had such a sad story and deserved better but other than that he also had sm potential to be a really good character. He already was to me tbh, I really loved him and bawled my eyes out when he died, but he definetly could've been even better. The writers did him dirty and I'll never forgive them for it.

•I know many ppl hate Gadreel so I think this is an
unpopular opinion. I think he was a very compelling character and I wish we could've seen more of him. He did bad things but his intentions weren't bad. At the end of the day he was just another manipulated angel that thought he was doing the right thing. He has a lot of history if you think about it, especially with Lucifer, so getting rid of someone like him so soon was really a shame imo. I would've loved to see him interact with Lucifer in s11 for the first time in who knows how long. He could've had a great redemption arc (unlike some unrealistic redemptions that some characters had) and could've been a good ally. I don't hate him for what he did tbh, I actually feel bad for him, I only hate Metatron.