The Crown, as prosecutor, must always prove that the accused committed whatever offence they are charged with, but “incrimination” occurs when the accused leads evidence, designed to exculpate them by (at least) raising an inference that someone else committed the crime that they are accused of.
It is different to the accused simply saying “it wasn’t me”; incrimination is “it wasn’t me, it was X who did it”.
The specific incriminee(s) must be named in the notice of special defence.
Where the incriminee is not a co-accused, incrimination is classed as a “special defence”, and, as such, the Crown must be given notice of it in advance.
Where the incriminee is a co-accused, incrimination is not technically classed as a special defence, but notice of it must still be given.