Iron maiden only charge you if you run too far away from her. Try to kite closer to her.
Iron Maiden and all human type enemies for that matter can spawn with random weapons. In one encounter she can barely deal much damage but in another encounter she can deal big damage because her weapon has Sinister prefix, which increases damage against humans.
About the topic of the thread, several threads were already made giving advice about the Kubacabra Nemesis. But unless you are a DoT build, you are gonna have a really tedious time against him currently, even you take the necessary precautions. Thankfully he will be less tedious (hopefully) in the upcoming patch.
The main problem with this guy IMO is that the blood pools should have a bigger CD and restore a little less health. You basically can’t stay still for more than 4 seconds against him, and that is frankly excessive, expecially when there are 3 or 4 copies at the same time.
4 sec is even too much. From my experience, even less is enough for him to heal. Which brings to hit and run tactics, abysmal character micromanagement, and incredibly long and tedious fights 
I agree, he’s very overtuned for all but a select few of optimized builds For me the fight is easy to cheese, go to the Gloom teleport and go east, keep reloading game until he’s at one of the 4 spawn points near the Gloom portal. When he is you just pull him back to the Rover NPC’s who can facetank indefinitely and you hit each one from behind until they’re all dead, easy. I hate cheesing it like this but even on a full tanked out Warder he hits way too hard.
Ok playing a two hand phys bleed warder with a bunch of internal trauma damage and I find kupa annoying but easily killable with a bit of kiting (because of DOT) But my god Grava is impossible for me right now met him a few times and the times I tried to fight him I just get killed within a few seconds and even with near max move speed I cant kite the guy. Out of everything I have met in expansion that guy is the one thing I feel is op.
I have just over 17K hp maxed resists a few over max and more than 2k armour yet this guy still 1 - 2 shots me just feels way over the top unless i am missing something.
I can tell you from my point of view from playing a vitality conjurer that Kubacabra is the easiest Nemesis by far but the only other one that I’ve killed in Ultimate has been Moosilauke. Technically, I’ve killed Benn’Jhar without dying but only because he in effect glitched because of terrain/geography. He’d normally destroy me. Valdaran can one-shot me. I’ve run into Kubacabra a half dozen times in the new Feral Thicket/Tainted Wood instances and had half the instance running after me including him and he’s went down easily even in that situation. Tactics: Range attack, dot, run - repeat until dead.
I still haven’t killed Gargabol but Kubacabra hasn’t been an issue yet. Moosilauke with all of his freezing attacks has been a lot more of a challenge unless I bring hoarfrost ointments.
You are a bit late to the party.
When this thread was created, Chupa fight was a fucking mess. Not anymore.
@Delta to give you perspective on what hellcat was talking about, even the tankiest of s&b builds can’t facetank him, especially the last phase. This was with exception of retaliation, but those builds almost can’t kill him due to the heals.
Kubacabra: Hit, run, heal and repeat. Kubacabra Clones: Hit, run, heal and repeat.
But if you can face tank him then great, I guess. It doesn’t really matter how you bring them down just as long as they go down.
During testing for the expansion I ran into him with my Conjurer in Ugdenbog and with all the spawns I ran and ran and ran. So far and so fast I actually outran his leash - and it’s a very long one! 
Don’t think Zantai quite believed it was possible. It was my first experience of his spawns too. Regrouped with the pets and crept back slowly tackling each one until they were all gone.
I ran him straight into that Rover outpost on the bend at the start of Gloomwald(?) or Ugdenbog(?). They were not impressed by that, but they did buy me the extra time I needed. A brief moment of watching someone else getting defiled by him.