Translation:That small, white bunny is really dangerous.
Pfffff. I don't get why this must be nominative in stead of partitive: does anyone know why?
Do you mean "todella vaarallinen"? I don't have a very good answer (the partitive is indeed a difficult case to pin down), but instead some example sentences, which might help. Or not.
"Se on todella vaarallinen." - It (a person, animal, thing) is really dangerous.
"Se on todella vaarallista." - It (doing a thing) is really dangerous.
"Makkara on kuuma." - The sausage (a countable thing) is hot.
"Kahvi on kuumaa". - The coffee (an uncountable thing) is hot.