I'll vouch for rainbow shark agression. But it all depends upon the size of the fish relative to each other, and the size of your tank to determine if some fish will get aong.
If you have enough bottom surface area of your tank, with plenty of hidy holes, then a rainbow shark and some cories may very well get along provided each has a side of the tank they can go to. The rainbow shark will stake out territory and chase -every- fish away from that one spot (usually a cave in a rock or under decor). Once the fish have exited its territory, the rainbow shark will break off and return to its hidy hole, and the other fish is left alone to peacefully go on its way to other parts of the tank.
The bigger the rainbow shark, the more territory it claims, thus the bigger the tank you will have to have.
Also, bigger fish pick on smaller fish, that is just nature's pecking order. If your cories are little babies unable to defend themselves or swim away fast enough from a large rainbow, expect the cories to suffer. But if the cories are big enough to swim away fast enough (and they have some place to go that is outside the rainbow's territory), they should survive just fine.
I currently have one rainbow shark living with three emerald green cories. My decor (carved rainbow rock) is stacked half-way up the tank. Amazingly my rainbow has decided it likes the territory mid-level in the tank, and chases my tetras around. The cories, being below the level of his territory, he leaves alone, and they swim about beneath him relatively undisturbed. I've even seen them swim into his hidy hole, and he'd not bother them unless they really bump him.
My cories and the rainbow shark are all relatively the same size. My rainbow shark is also very young (only 1/2 the length of my pinky finger). It was also the smallest, most submissive of the fish in the tank at the shop, that's why I grabbed him. Although, for health reasons, it is always best to pick the healthiest, most active fish, and that fish is usually a dominate member of that species. He may grow more agressive as he gets older.
This works for me, I cannot promise the combination will work for you, but you can try. Worst come to worst, you remove the aggressor and give him is own tank.
~~Colesea
