Max on weaken??

200%. You can increase this cap by Epiphany(5) too so you’ll get up to 250% on one character. With (8), really up to 280%. It sounds way overkill though. You are good with 90% though for the vast majority of cases, even immunes will only resist by 10% rather than be 100% immune. 90% of the time triggering vs 100% doesn’t sound like a guarantee but 9/10 triggers is pretty good for the potential boost it gives you.

Excluding cap, ascendant applies a weaken-like effect of reducing resists via arcane. so 200% weaken +62.5% reduce resists can do -262.5% to their resists. Potentially +262.5% in dmg best case.
Ascendant seems to combine from hirling as well, I’ve even observed weaken kinda does that as well. Though that could be just placebo or brutal overkill when I was testing with a chakram test rogue. Ascendant does combine though. Possibly even Effective Mythic. Imagine 200% weaken per char + ascendant each as well. That’s a fun thought experiment.

Another brutal or epic combo, an easy dps maker is arcanist + weaken. 20% ED per weakened enemy :open_mouth: . Doesn’t even need Ascendant for it, weaken applys arcane debuff :+1: . It was OP before with crits but I think its probably even better with 20% ED vs the 20% Total DMG per enemy. Can confirm for some easy dps with frozen as well. Crushing flames or any type. Weaken applying the debuff is all it took.
I did find diminishing returns with Effective with higher weaken though. Sometimes its worse, or better.

The other fun thought experiment is the max possible ed% you can get on gear, then a set like permafrost or inferno, arcanists effect per enemy, elements 10% nature per gear. 600% ED (or 1200%) +60% ED from all the natures, 20% from pet (or 40% eternal pet), 75% permafrost, Not to forget a Talent such as Might 20% on warrior, and say 15 enemies effected by arcanist. Even just half or a 3rd of that such as 200% ED on gear instead of 600%, as 600% may seem overkill.