What does Willpower actually do for a psyker?

[Ninth Hour]

In the original 40K RPG's by Fantasy Flight, Willpower was basically "the psyker stat", as the vast majority of powers, in all schools, scaled according to it and Psy Rating.

So it was quite jarring to realize that it actually has a much smaller role in this game. Most of the psyker powers seem to depend only on Psy Rating (and Resolve, if Sanctic). And on enemies failing their WP resistance tests.

As far as I can tell, the psyker's Willpower bonus does not factor into any of the powers- other than Psychic Shriek (and by extension Psychic assault), some defensive Divination buffs, and the Warp burn for pyromancy attacks. Some of the passive Psyker talents are also affected by Willpower bonus...and that's it. You don't seem to get much out of WP if you don't have Divination or Pyromancy school (and even in the latter, the impact of WP seems to be only for the DOT's, rather than direct damage),.

Am I interpreting this correctly? Despite my hundreds of hours in the game, I have yet to advance past Chapter 2, so I do not know if anything changes later (most of my hours were from the Alpha, Beta, and replays of the early chapters) .

If this is the extent of Willpower's role, then I may have been building my Sanctic psyker officer incorrectly. Instead of concentrating on Fellowship and Willpower, I may have been better off with Fellowship and either Ballistic skill, Agility, or Toughness. Willpower for this character seems to only have value for passing resistance tests.

Even the psyker staves- including the vaunted Sanctic staff- don't include Willpower bonus in their damage calculations. Pretty counterintuitive for someone conditioned by the original RPG.

[Pixie1001]

I think they wanted to make psykers more multiclass flexible, so you could do things like a sanctic warrior that still has enough stat points to fill out their strength, toughness and weapon skill, while still supporting more 'pure mage' builds like soldier or operatic telepaths that forgo BS/WS for WP.

That being said, most pure psyker builds will end up wanting Willpower anyway, since you end up with like 3 different disciplines, meaning eventually you'll end up wanting to use psychic assault, divination buffs or iron arms.

For your specific build where I assume you're mostly just giving all your AP away to Argenta, another stat like agility or strength for more defence might've been better though.

[Balekai]

It depends on the sub psyker origin. Some of them are very heavily focused on Psy Rating + Willpower, and others Psy Rating + mix of say PER/WILL like Diviner for example. Of course some of these psyker schoold could have used some more Willpower dependency, but there's some interesting synergies opened up by various abilities/talents using various characteristics.

Then there's Sanctic Psyker which is its own beast.

A unique Psyker School that's based off Psy Rating and Resolve. Meaning it's the friendliest least characteristic dependent Psyker or even Origin in the game. All you need to do is increase Psy Rating and Resolve which it allows you to do by itself (Psy Levels, Psalms of Heroes, Word of the Emperor) and can be done with other abilities/talents, without even needing Fellowship investment (but of course, benefits from such as that increases Resolve).

It also scales and gets better as a fight gets more protracted, sort of representing the eternal struggle/resolve of the Emperor channelled through the character. That said there was probably room somewhere for Willpower here in order to make this school not so anti MAD.

[tempest.of.emptiness]

Here's a list of WP-affected Psyker talents and abilities, with a partial description of each highlighting the impact of WP:

General Psyker Talents:
● Still Mind - boosts resolve by WP bonus / 2 (Note that with this even Sanctic Psyker benefits from increased WP.)

Biomancer Psyker Abilities and Talents:
● Invigorate - restores (2 x PR + WP bonus) wounds
● Regeneration - recover (PR + (WP bonus / 2)) wounds each turn
● Pulse of Life - heals gain (5 + 2 x WP bonus)% crit chance

Diviner Psyker Abilities:
● Foreboding - Target's dodge cannot be less than psyker's (PER bonus + WP bonus)%

Pyromancer Psyker Abilities:
● Ignite - damage range of (1 + 5 x PR)-to-(WP bonus + 5 x PR) and warp burn of (WP bonus + 2 x PR) per turn
● Firestorm - inflicts Ignite (so WP impact is the same)
● Orchestrate Flames - prevents warp burn from ending, the damage of which is influenced by WP bonus
● Molten Beam - deals double Ignite damage and inflicts warp burn as Ignite (so also impacted by WP)
● Incinerate - deals double Ignite damage (so also impacted by WP) and bonus damage based on burn effects in play (including warp burn, so impacted by WP in cases where anyone is currently warp burning)

Telepath Psyker Abilities:
● Psychic Shriek - damage range of ( 1 + WP bonus x PR)-to-(4 + WP bonus x (1 + PR))
● Psychic Assault - deals Psychic Shriek damage (so WP impact is the same)
● Mind Bond - targets can use Psyker's WP to make willpower tests if it is higher

It is certainly possible to make a Psyker whose abilities and talents gain nothing from WP (Sanctic without Still Mind is the simplest example, but there are others). It is also possible to make a Psyker whose WP has some impact on their effectiveness without it being critical to their success (Diviner with Foreboding is an easy example).

However, I think that most Psyker builds are going to have medium-to-heavy impact of WP on their effectiveness, and are going to feel pressure to boost WP to gain the corresponding benefit. Pyromancer (except for builds using Pyromancer for talents and not using it for damage) and damage-focused Telepaths are the strongest cases for this. The impact on healer Biomancer is pronounced; I suppose you could skip WP but that will limit your heals greatly. Even Sanctic psyker should probably take Still Mind and boost WP unless your build absolutely cannot afford to boost WP.