I think my disappointment in the PW is just that the -2 ability is so mediocre. I normally only run 1x of any PW because they're often so easy to deal with, meaning that more often than not, their ultimate abilities are totally irrelevant. That said, I would argue Vraska has more uses simply because at that point in a G/B curve, you should be hitting something that can perform multiple removal and protect itself - both of which she does in spades. Even Jace, Memory Adept's second ability can be very useful, but to make two creatures fight? I'm just not feeling it. I could be wrong, it certainly wouldn't be the first or the last time, but I'm not seeing where it'll make that big of a dent in things.
For Borborygmos, I'm having thoughts of Conjurer's Closet paired with Gatecreeper Vine and Borderland Ranger to simply just mess things up once you get him on the field.
Aurelia can be useful in the sense that some well timed flickering can actually result in more than two attack phases. I actually spoke with a level 1 judge on the topic and asked if you use Cloudshift on her at the resolution of the first attack phase (before damage is dealt) but after her trigger hits, would she be able to attack in the second attack phase and generate a third one. He said that because she technically leaves the battlefield, her attack in the second attack phase would count as though it were her first attack that turn, meaning you would get a third attack phase. Pair that with a few other pieces and you can imagine things get pretty nasty, but that's the only combo where I see her being all that powerful. But she could make for quite the useful piece doing that in a red deck dedicated to using their own creatures against them (could Tibalt actually have a place?).
The Omniscience combo would be nice, but really, that's 21 mana across two turns... I'm just not seeing where you're going to hit that and still be alive - at least not unless they make ANOTHER ramp defender to go with Axebane Guardian. Otherwise you'd do it once and BAM, they'll be onto you and kill the rampers.
Hellkite clearly was designed for Modern and other formats to deal with people abusing affinity. For Standard, it's a waste of space.