Some extra options and innovations for the Immortal Selig Whirlwinder
Since the build is functionally unkillable until extremely high Pit levels, there have been a few ideas I've been cooking up to make it just a bit stronger in some areas.
One is replacing the Aspect of Heavenly Strength's huge damage reduction for an even stronger one that doesn't take up an aspect: Igni-Lac with Challenging Shout upgrades. For those unaware, invoked skills do benefit from skill upgrades if you're of the class that has access to said skills. This means that the invoked Challenging Shout can have its duration extended by the Duration Bonus side upgrade, resulting in full uptime with Igni ritual rune. Bawl skill upgrade for Challenging Shout adds another 20% damage reduction (with an over time decay), however since the invoked skill is only about half the duration, the effect decay rate doesn't become severe enough to dissappear. It can also contribute to damage with Damage Bonus side upgrade so it's defensively similar to Heavenly Strength aspect but offers an offensive boost, enabling either freeing up an armor slot OR doubling down on Heavenly Strength aspect to tank into further pit levels than ever.
Another is more of a side grade which is replacing Ghor's with Bane of Adjed Den and wearing Rage of Harragoth. Due to sheer number of hits occurring via WW spin2win, dust devils, and Mighty Throw pulses, the auto-cast Mighty Throw is rapid fire from RoH's cooldown reduction chances via slottijg 2-Handwd Sword Expertise as your technique, and gains Channeling aspect boosts since the auto casts occur during WW channeling and thus doesn't interrupt it. Mighty Throw also being a Martial skill means that +Martial effects boosting WW will also boost the auto-throws.
One more extremely exploitable thing that can be used is Neo ritual rune, since the Selig Fury buffer means the immortal Barb never takes hp damage so its just free 200 invocation per 2 secs. But what invocation use it on? How about Ner, with Tibault's Will. Proccing Ner activated Tibault, giving a damage boost on pants AND, the big jackpot, a whopping 50 Fury regen. I'm not 100% sure on if there's a minimum duration for Unstopppable, but there is at a minimum of 1 second, then this will result in full uptime Tibault boost (1 sec + 5 seconds after). Or if there isn't a minimum duration, then there will be a 1 second vulnerability period. If the prior, then this might be able to replace Fury regen gear entirely. But if there is no 1 second minimum then this can end up risky.
Any other ideas to push the immortal Barb further?