I think the bichir and butterflies fit that bill for oddball.
Imo, dithers are necessary for any tank (excluding where they will be eaten). They help to bring out natural behavior of larger fishes as well as give you something to look at. Most oddballs tend to be more cryptic.
What about Pike topminnows? Those look awesome, and they are appropriate size-wise. I may have to ditch the butterflies though if I did topminnows.
I like the crypticness of oddballs. They add a sense of mystery that many fish do not have. A little story about the oddness of oddballs: My tank is in my bedroom, and every night, all my nighttime fish (3/4 of my stock lol) come out to play. I have a Fluval heater that produces a bright blue light, and usually, my BGK swims vertically in front of the light, casting a massive ghostly shadow on my wall. You can see the silhouette of my knife and the intricate fin movements (the rippling effect) move up and down in front of the light. I love it.