Does the rogue feat The Harder They Fall trigger when you use the fighter feat Improved Knockdown?

[RandomTallGuy]

Basically the title. There's three schools of thought.

A) The Harder They Fall would not trigger when you use Improved Knockdown, only regular Knockdown, because the Improved Knockdown feat only applies the critical success effect of a trip. This doesn't mean you "critically succeed at tripping a foe", only that you get to apply the "critical success" effect under the "trip" action to your strike.

B) The Harder They Fall would trigger when you use Improved Knockdown, as the effects of The Harder They Fall are now part of the "critical success effect of a trip".

C) The Harder They Fall would trigger when you use Improved Knockdown, because any action which applies the success or critical success effects of an action counts as succeeding or critically succeeding at that action for the purpose of feats related to that action, respectively.

[Castilliano]

Since it's a corner case, you'd have to ask your GM. I'd be amazed if they didn't allow it by sticking to some obscene levels of rules idolatry. (And I'd take that as a red flag re: their GMing as a whole.)

IMO, Improved Knockdown contains a Trip.
For one because the feat says you're doing the Knockdown action and that's a Strike then Trip. You're just combining them into one roll in the Improved version and getting the trip result upgraded. Trip is still embedded.
For two because you are tripping them. The feat could have used the "knocks prone" language some other abilities have, but it doesn't. You might not be specifically using the Trip action (or as a sub-action), but you are tripping when you get the "critical success effect of a Trip", it's just automatic w/ a Strike.

Now if The Harder They Fall had more particular phrasing there might be an issue, but it's just asking you to trip them, which you'd be doing.

[The Raven Black]

If you had only Knockdown (and The harder they fall) and got a success, you would apply additional damage and sneak attack on a critical.

If you do not consider that Improved Knockdown gives you a result of critical success but only its bare effects (not triggering the additional damage and sneak attack of The harder they fall), then you do not get ANY additional damage on Improved Knockdown. Which then becomes objectively worse than Knockdown.

Definitely not RAI IMO. So I would rule that the additional damage and sneak apply on Improved Knockdown.

[HammerJack]

I don't think obscene Rules Idolatry is needed for this one to not work. Improved Knockdown not including a Trip is part of what makes it such a big upgrade. Being a single Strike with extra effects, not a Strike and a Trip that use the same roll means that it is only one Attack action, so you don't have maximum MAP afterwards, like you do with regular Knockdown. If a big consistent upside comes with a niche downside... that actually seems like a reasonable ruling.

[Darksol the Painbringer]

The Raven Black wrote:

If you had only Knockdown (and The harder they fall) and got a success, you would apply additional damage and sneak attack on a critical.

If you do not consider that Improved Knockdown gives you a result of critical success but only its bare effects (not triggering the additional damage and sneak attack of The harder they fall), then you do not get ANY additional damage on Improved Knockdown. Which then becomes objectively worse than Knockdown.

Definitely not RAI IMO. So I would rule that the additional damage and sneak apply on Improved Knockdown.

If they apply, then how does it work? Does it apply 1D6+Weapon Dice+Sneak Dice?