A Lisa Frank Rainbow Angel Kitten
This costume idea is so good that I might take it for myself. Your base is going to be a white cat. So you can wear white pants/shirt or a white minidress if you feel the need to make the costume "sexy", or maybe some white flannel pajamas for coziness! Then, I guess what I would do is get some white cat ears (FROM A STORE!) and some wings of some sort. You're going to want to turn the wings rainbow colored, if you're going to be historically accurate. I think I would probably make mine out of cardboard and paint them. But I seize crafting opportunities.
Ok so you should know this, but if you don't, Bunnicula is a vampire bunny who sucks the juice out of vegetables!! To be historically accurate, the first book came out in 1979 but as its a part of my 90s consciousness, it is allowed on the list. Your base for this costume would be a rabbit, so all you really need are ears. And vampire teeth. If you naturally have a widow's peak hairline, like I do, then even better.
Peggy & Al Bundy
This is a two person costume.
The older I get, the more I love Peggy. Her outfits were on point, those kitten heeled mules, high waisted spandex, belted sweaters and that huge hair. If you're lucky enough to have naturally red hair then just tease your hair within an inch of it's life and liberally apply hair spray. The clothing shouldn't be too hard to come up with, since the 90s are back and we all seem to own some element of a Peggy Bundy outfit, though perhaps we've never worn all the components at the same time.
Al Bundy - you need a willing Al Bundy. The real Al Bundy would never agree to go to a party with you, let alone in a couples costume, but hopefully your Halloween buddy has slightly more zest for life than their costume inspiration. Al wore a lot of beige, and ties and a pale blue shirt usually. A look of general disdain will go a long way in making this costume feel really authentic.
A few years ago, on Halloween I saw a guy dressed perfectly as Daria. It was amazing and I wish I had taken a photo.
Speaking of Daria, that's another simple costume. Again, attitude is key.
Green Jacket, Mustard yellow shirt, black pleated skirt, combat boots and round thick-rimmed glasses. And apathy.