Why not have the heart make her count as a lvl 3 psyched for the purposes of deny the witch rolls? Then she can have a rather strong resistance without being fully immune and allow her to benefit from friendly powers too
That would probably be fine (especially if she generated additional warp charges for you to deny with), but it would also be considerably less potent of a psychic defense than she used to be. It would probably call for a points decrease. To break down my version of Malys, she basically has...
*The statline of an archon but no pistol option. Let's say that puts her at the starting cost of an archon.
*A 4+ invulnerable save. So basically the cost of a clone field.
*A djinn blade. And let's face it, no one
really likes the djinn blade. Most people would rather have the husk blade or maybe some sort of ranged weapon. So let's say the djinn blade's cost, but keep in mind what you're passing on to get it.
*A close combat weapon for the bonus attack. No additional cost; this actually less useful than the pistol the archon normally has.
*Clockwork Mind + Labyrinthine Cunning. Which is pretty darn good. Assuming the bonus trait is randomized, call it 30 points?
I don't have my codex in front of me, but I want to say that comes out to about... 120. So about 120, but as previously pointed out a generic archon can take a better wargear loadout. So now let's look at possible ways of handling the heart:
*Psy Level 3 (defensive only; possibly generating extra warp charges). Best case scenario, you'd be denying on a 4+, but there are plenty of Level 3 (and even a Level 4 or two)psykers out there. Being a higher mastery level would still only help her unit, but it would be far less effective at it than the old heart. Considering the best case scenario is that you ignore 50% of the enemy's successes, and only when they're targeting one specific unit in your entire army, I'd probably only rate that at a cost of 5 or 10 points.
*Immune to all powers (friend and foe). Makes it so that her squad can't get witchfired to death. Which isn't super common in my experience, but it does keep her safe from things like cleansing flame and helps you deliver, say, a unit of incubi relatively safely. Keeps her (and her squad) from benefitting from things like fortune or protect, so those same incubi are hard to supercharge with eldar allies. Also keeps shadowseer allies from giving her squad stealth + shrouded. The downsides here are situational (if you're taking Malys, you're not planning on buffing her unit with psykers), but not being able to witchfire or maledict a single unit in the army generally isn't too big a deal. Especially since Malys isn't exactly a wreckin ball. 10-15 points?
*Immune to enemy powers only. As the last one, but you can now make a mini-star with beefed up inubi or maybe a boosted court of the archon or something. Maybe even toss her in with some shadow seer protected harlequins. This is decidedly more powerful than the last option, but the real threat here is the mini-star as opposed to the heart itself. It seems like relatively few armies would be trying to answer such a mini-star exclusively with psychic abilities. Sure, GK would like to psychic it to death, but they'll still have force, hammerhand, and their non-psychic offense to fall back on. Most other armies don't really rely on psykers for their dakka; using them instead as a nice bonus (and they can still have that psyker blast other stuff in your army). Tzeentch daemons are the only thing that really comes to mind as having trouble against the hypothetical mini-star, and they'll have enough psychic dice to shut down your psychic buffs anyway. So all in all, I'm inclined to say that the cost of this version is
at most 20 points, but that feels pretty high for psychic protection on a single squad.
Thoughts?