There are a couple of odd things that happen when agnon kills Pontifex using hardened assault.
1). Agnon doesn't wait around to take a second or third attack against ponti's skeleton form. This one may be intended, but it doesn't act the same against Chromus or killing a shade possessed character. In either of those cases, agnon waits for the animation to end, then resumes attacking.
2). When killing Pontifex, he also never assumes his graniteform. It seems like Ponti's animation interrupts agnon enough that he stops his turn.