Deadly follow-up?

[Mr Whos]

In the UC under the Kensai archetype it says "the following magus arcana complement the Kensai archetype" deadly follow-up is one of them.
My question is what is it? I cant find it in any of the books.

[Gauss]

Probably an ability that never made it into print and they forgot to remove it from that list. In the next errata that will probably get removed sometime in the future.

- Gauss

[Psion deXanthus, Inquistor]

Wasn't there a feat called Deadly Follow-Up?