Yeah, this is a pretty good list. Just had some thoughts about it:
The website 'Wicked Horror' immediately made me think of Faith. 🙂 So half these guys could've appeared on her show-that-never-was.
Der Kinderstod: Definitly see this. A sneaky, creepy invisible monster that targets you when you're sick? Perfect fodder for another episode imo. Something like this could've targeted Dawn (maybe drawn to her key-ness' somehow) when she was poorly. Buffy could've had a pretty good rematch protecting her sister from invisible death.
Kakistos: If you read 'Go Ask Malice' then it becomes clear that this guy, Faith's first 'Big Bad' if you like, was waay scarier than the Master, on so many levels. He's older, more powerful and has distinctly horrible things he does to those he captures....
This guy could've had a two-parter in S3 or could've appeared in flashbacks about Faith's Boston days- either way it could've been brilliant.
Btw- In the novel Faith almost split Kakistos' head in two vertically with a thrown axe. Badass! 🙂
Norman Pfister: Actually the Order Of Taraka in general should've returned in either show. Why didn't W&H hire these guys to kill Angel at least once? Would've been a nice callback to s2. These guys were meant to be big enough to frighten both Giles and Angel, so they should've had more of an impact on the wider world, logically speaking.
Sunday: YES! I really liked Sunday, the only vampire who could've probably out-snarked Spike. If you wanted to have a chipped vampire running around S4 it could've been her. Or at least have her hook up with Spike instead of Harmony.
Harmony...urgh. 🙁
Marcie Ross: I don't think she should've appeared back to Buffy (unless it was as some sort of scout for the Initiative...) but the focus of her rage was always Cordelia. She should've showed up on Angel to try and terrorize her all over again (she was pretty nuts and being trained as an assassin), in the process showing how much Cordelia has changed from S1 of Buffy, and how she's now a decent person. Would've been a nice Cordy-centric episode in S2 (where they don't have Angel around to help) or S3.
We got to see Buffy fight invisible foes but never Angel.
Ted: At first I disagreed with this- I'm not a huge fan of the concept of Ted in the first place. But it really could've worked if done right.
Picture in S4 that Joyce is slowly being stalked in an, intrusive, creepy way over a number of episodes. But its not a vampire doing anything, its a severly damaged Ted come back from wherever (how did Buffy dispose of a big, burly robot-body before her Mom woke up? Bury him? Take him to the town dump to be recycled?). We would've seen a little more of Joyce in S4 before they made her sick.
Or maybe Ted comes back to find that Joyce is passed on and lashes out in homicidal rage at the remaining Summers girls?
Dracula: I think I'm one of the few that actually liked Dracula's appearance on Buffy (and it could've been so much worse. Freddie Prinze, Jr as Dracula anybody?) but I'm cool with him just being in one episode. We have the comics for his return.
The Gnarl: I guess, but since he was in S7 of Buffy he would've had to return on some other show, like Faith tVS for example. Other than that I agree that he was one of the scariest, most effective MotW villains we'd seen since S4.
Although I quite liked the Gargamfasman...the thing that drove Buffy insane in 'Normal Again'.
Whistler: Him returning in A&F as a big Bad was pretty cool, and we had Doyle to be Angel's guide. To be honest I don't miss him- I just wish we'd had a better explanation of who he was on Angel's show.
The Gentlemen: This is the only one I really disagree with. These guys were great, creeepy, horrifying. But they had a particular schtick- silence- which would've been easy to figure out if they had returned to the show (plus another silent episode would've been too gimmick-y).
The only way they could've made a reappearance is if the Buffy writers had done what was done with the Weeping Angels on Dr. Who and expanded on what/who the Gentlemen were- and that's never really been Buffy's style with returning monsters (apart from vampires of course).
However- they could've turned up on Angel no problem. LA swallowed in silence could've been far more chaotic than Sunnydale. Thougt I imagine Wesley would've figured things out a bit sooner than Giles did, for he is book-man.
Man, that was a long post. 🙂