Y'know, flat out, with what is out, it is a stunning missed chance that Ashiok has nothing to do with the story.
Theoretically Ashiok would fit the Hellraiser aesthetic to keep the theme, but instead Ashiok got utterly wasted in the last Eldraine.

Which makes me want to weigh exactly who I would have put in that place, because the Eldraine story was something of a nothing burger anyway.

I'm just really dissatisfied with their tactical deployment of characters lately.
Heck, I like Ral, but he was running three stories in a row.

I think Ashiok would be overkill since this is the nightmare plane, though I suppose a struggle to wrestle power from Valgavoth could be interesting