hybrid belfry
This is only an hypothesis that Dampener is to blame as it's a new item that I assume he steals.
Mthrix took literally 1 damage from all sources and Capacitor I think dealt 26 which would indicate he had obscene amount of armour, effectively making the fight over ten times longer.
It was multiplayer lobby so I don't know the Dampener count but probably 25 or more plus some shield gens and Transcendence. The total HP pool may have also contributed to why it seemed absurdly long.
versed valve
"Anything you say will be used againstyou"
distant lagoon
25 dampeners would be 750 armor, ~88% reduction and effectively giving him 7.5x health on top of the health buff from transcendence and psg, so that checks out tbh. Especially if he also had some stacks of 
it would be a painful fight but doesn't seem like a bug
hybrid belfry
The category of bug here is unintentional changes to the boss's design. He's meant to periodically deal 8% hp self damage and tougher times is black listed. Essentially things that drag the fight out too much from the base amount, an oversight.
versed valve
i thought armor was 100:50% 300:75% 700:87.5%
distant lagoon
i thought armor was 100:50% 300:75% 700:87.5%
that is correct
but 750 armor is 88.24%
versed valve
how about 2147483647 armor?
versed valve
This is only an hypothesis that Dampener is to blame as it's a new item that I a...
why did you get many shield items then?
distant lagoon
how about 2147483647 armor?
this is what the wiki's calculator says
damage always has a minimum of 1 so technically you can never have 100% reduction, even with integer limit shenanigans
versed valve
got it. and -2147483647 armor?
distant lagoon
-99.99%
negative armor can't go past +100% damage
versed valve
how about, 20 psgs - dampener