Vraska, Relic Seeker has really impressed me as a planeswalker. She really is one of the top-tier options - she's an answer to 3 different permanent types, cranks out pretty solid tokens, and has an amazing starting loyalty.
This deck is built as a pretty standard ramp/bomb/control affair, running pretty much all the spiciest bombs GB has to offer in standard. Many of the cards in the deck are of the "must answer" variety, with lots and lots of ways to grind out value in the long game. Vraska doesn't have a lot of particular synergy with the deck, but she is a powerful wincon and answer in her own right - so she fits comfortably alongside everything else the deck is doing.
Bontu's Last Reckoning seems good here. I think you're going to to need a proper board-wipe, even if it comes with a disadvantage.
Yeah, that was one of my last cuts. I confess I haven't played any of the "lasts" yet in commander, but my sense is that skipping the untap is going to really really suck if you aren't already at 9 mana or so. Especially since you obviously won't have much in terms of board presence afterwards. If I was going relatively light on creatures I'd still do it, but this is a pretty creature-heavy deck, so I think I'd rather just fight for the board and play targeted removal.
I think besides 3(?) cards (arterial, naturalize, bestiary), everything in my deck either is a creature, becomes/creates a creature(s), or kills a creature. So I think it'll be rare that I'll really want a board wipe, let alone at such a steep cost.
Got to test this out tonight in a couple 3-man games vs 2 commander opponents. First game went hilariously - one guy played necropotence and later kuro, pitlord when I had mirage mirror in play, and I got a bunch of nearly free cards and then ripped his board to pieces when he was too low on life to do much of anything about it.
Second game went much longer. Early on it was neck and neck between me and teysa, with teysa playing multiple anthems (spear of heliod and eldrazi monument) with token producers, but I managed to ramp up enough that I could cast vraska multiple times to kill both of them and then dropped a board-wiping demon of dark schemes which was sadly removed. it was then pretty close (although I was building up better and better resources) until I finally dug to my liliana, which reanimated the demon and blew up the board AGAIN giving me 27 total energy which I then proceeded to use to reanimate damn near everying I could. Keeping teysa off the board was difficult, but I was able to keep it alive long enough to generate absurd board value while protecting both planeswalkers. Sandwurm convergence came down, and even when creatures all got exiled I was generating way too much value to be stopped and they were both out of hands. Killed teysa with some vehicles and a few wurm hits, and then ulted vraska to kill the other player (mathas, who was getting close to 100 life and hiding behind taxing enchantments). It was basically 2v1 for the better part of several hours and the deck just straight-up out-valued them both. There's just so much value generation in this deck it gets completely out of hand. Vraska herself was extremely clutch as a way to kill anything from the command zone, which she did over and over, and a way to generate value, and as a wincon even if the opponent has massive life and defenses.
I had subbed in a jadelight ranger for yahenni because I couldn't find him, and I REALLY wished I'd had him. Having a sac outlet to repeatedly reanimate noxious gearhulk would have been the stone nuts, plus I could have protected creatures from exile so lili could reanimate them all over again.
Definitely did not feel the need for bontu's, but ofc that was just 2 games and not even really brawl so it's not much of a test.