Between the necessary rules change, the templating issues, and the fact that Split Second has a pretty low baserate for making any returns at all, this seems like it should be quite low.

Do reprints count?

@AndrewSabisky Irrelevant, since no existing cards satisfy the criterion.

@IsaacKing oh I misread the question

I assume it doesn't count if they print an activated ability with the same effect as split second but not spelling out the keyword. What about a silver-bordered variant of split second like "just a second" as on Slaying Mantis?

@AlexChurchill It has to actually be called "split second", not just do the same thing.