The Yncarne's very presence repels the ufathomable and higher-dimensional realm of the Warp itself.
"The howling, screaming vortex through which the Reborn passed was the embodiment of utter Chaos. So fierce and baleful was this passageway it would have robbed the sanity of a lesser being in a matter of moments. Yet the Reborn found themselves floating through a tunnel in the Warp unhindered, as if borne by an underwater current. At their fore was the Yncarne, a revenant creature so inimical to Chaos that the stuff of the Empyrean could not slow it. Even the Gods of Chaos did not look upon the creature directly; the incarnation of Ynnead's essence was so anathema to them they could not truly perceive it, even had they known where to look."
The Yncarne completely and utterly kills a Haemonculus by flexing a finger. Not only does it destroy his main body, but also all pieces of himself he had back in Commoragh, which is a series of pocket realms already contained within a larger alternate realm to the one the Yncarne was in.
"A moment before the Visarch came apart, the Yncarne burst from the morass of dead Pain Engines with a deafening roar of triumph. With nothing more than its bare hands, the avatar ripped apart djinn-spirits to dissipating wisps of ectoplasm. It flexed a slender claw, and the djinn's Haemonculus maste withered away to a puff of dust. In far Commorragh, those samples of the Coven-lord's anatomy that were kept for regrowth turned to dust at the same instant. There could be no proof nor safeguard against the death brought by the Yncarne, for it was the God of the Dead given form."
The Yncarne perma-kills daemons (and in the Eye of Terror, no less). Anyone remotely familiar with the setting will tell you this is something that is in most cases impossible, yet the Yncarne achieves it.
"A heartbeat later the Yncarne burst like a phoenix from beneath the Queen of Suffering, reborn in a fountain of ice-blue energies. It held a long and shining Cronesword in both hands, and as it soared into the sky, it cut the Daemon queen in half from groin to neck. The deathly energies around it lent it speed; in a blur of purple-white motion, it hacked and slashed at the Greater Daemons until they had discorporated altogether. The weapon wielded by the avatar of Ynnead was Vilith-zhar, the Sword of Souls, largest and most powerful of the Croneswords. After millennia in slumber, its edge was hungry for the blood of the Eldar's persecutors. Like a bladed whirlwind, the Yncarne plunged into the Slaaneshi horde. Its every breath was a killing mist, its every thrust the final death of a shrieking daemon."
So yeah. Going with the Yncarne.