There's a certain element of randomness to the whole thing, as some Diablo 4 dungeons are apparently more conducive to massive damage stacking than others. 'And the more crits that we hit in Grizzly Rage, the more this additive crit damage multiplier is going to stack up. 'With this build, we are stacking well over 1,000% crit damage to enemies,' Moxsy says in his video explainer. The tl dr, as he put it, is that the build deals 'constant big critical strike hits that double dip on damage modifiers and constantly trigger area-of-effect lightning damage.' Stormclaw Aspect makes Shred critical strikes deal a big percentage of the damage as Lightning damage to enemies around you, and when it triggers (all the time with Waxing Gibbous) it double dips on damage multipliers-which you stack with all your other gear, skill points, and Paragon points.Aspect of the Rampaging Werebeast stacks critical strike damage for every critical strike you get while in Grizzly Rage (which is all the time with Waxing Gibbous).Dire Wolf's aspect makes Grizzly Rage (Druid ultimate skill) reduce Shred Spirit cost so you can spam it.Waxing Gibbous axe to guarantee Shred crit strikes.There's a lot of complexity involved in pulling it all together, which Moxsy breaks down in detail in a build at DPS Check, but our in-house Diablo 4 pro Tyler Colp laid it out for me like this:

So how can this kind of mega-deletion damage be possible? It's not a bug or an exploit, but a carefully crafted build that takes advantage of legendary item aspects and 'double-dipping' to stack increasingly massive amounts of damage in the Shred attack.

Diablo 2 druid leveling guide