Lost a huge chunk of xp to Uber Atziri

Dear GGG. I recall reading that there is no longer an XP penalty for dying to Uber Bosses. Figured this would be the league that I finally get my 4 void stones as a solo TL player. Indeed, I verified no XP loss learning Shaper, Elder, Eater, and some of the other pinnacle bosses. Nearly got there on my first attempt of Maven; thought about going again, but that quest says to do Shaper in Elder's realm. I figured out and collected 3 of the summon fragments, then went to tackle Uber Atziri blind. I then proceeded to get absolutely crushed and stubbornly lost 50% of my 96-97 level dying over and over trying to figure out what was killing me. I guess she's not considered a pinnacle boss, although very new to me.

Sincerely,

- Frustrated

Atziri is not one you go into blind. It's one of the few bosses that are damn near impossible to learn if you don't already know about it ahead of time.

One of the four duplicates that get spawned holds a mirror, and it deals 100% reflected damage of both types. You basically cannot win without dying if you have an AoE attack and no reflect immunity. And there's really no way for you to "see" this in the fight.

BUT once you do get reflect immunity, she turns into the easiest boss in the game.

Here's the list from the wiki:

Players can no longer gain or lose experience in the following areas: Absence of Mercy and Empathy, Absence of Patience and Wisdom, Absence of Symmetry and Harmony, Absence of Value and Meaning, Crux of Nothingness, Eye of the Storm, Polaric Void, Seething Chyme, The Sacred Grove, The Shaper's Realm, and The Maven's Crucible.

The hyperlinks are on this page:
https://www.poewiki.net/wiki/Experience
Down the bottom in the version history section.

It is a bit confusing which it includes. I read someone saying the lost xp on uber cortex, not sure if that is covered.

I think they could potentially extend it to a few more bosses. The delve bosses don't have it either, I think it is mainly for ones that were blocking peoples progression.

Yea sorry about that, Atziri is a no go without reflect immunity.

If you dont have a mageblood, get a chest with reflect immunity, or if you have easy access to the mastry node that gives some, you can use a ring + mastery. Always a good idea to grab the pantheon as well, as even at 100% reflect immune, any increase to damage taken will push the reflect over the 100%

(Edit build specific advice:

I took a look at your profile and assume you are playing with your RF Chieftain. The only things I can see on your build that might be causing reflect on you, are your frost blink, shield charge and tempest shield. Whether you are doing enough damage with them to be a problem during the reflect phase, i'm not sure. You can probably beat this phase with this build, but if you find it is dying, you might need to adjust a few of those things during the fight.

The other thing is your curse. It doesn't look like you are using elemental reduction curses, which would be a problem with your RF, if not over capped. However, the punishment may still be causing problems if it is going on you. If you are ever getting to low life, you will be taking 60% increased damage, which is not good for RF where you are always taking a large amount of DOT, and just not good in general. There are some options with dealing with this if it is increasing the difficulty of the fight. A different curse, no curse, curse mitigation, staying above low life with flasks etc.
)

Yeah as the others are pointing out, the thing that you might of not realised you were dying to in the atziri fight is likely reflect.

She has 3 phases that continuously rotate until you get her. The starting phase, where she is alone and cast all her abilities, largely fire damage. One where she is in the middle with minions spawning from the four corners that you need to kill. This is not a dangerous area, prevent the minions from getting to her, as I believe they recharge her or power her up in some way. The other one, she becomes 4 separate versions that all act differently and attack at once. To beat this phase and get back to the starting phase, you need to kill any one of the four.

They all look slightly different and they don't span in the same location. One of them, is holding her shield up to the sky in one hand. That one does reflect damage. So if you don't have reflect immunity or mitigation, or a build that can handle reflect, like minions, mines/traps, proxies, DOT, and hit it at any time, you will almost certainly die. You may of noticed this if you have ever ran a map with reflect mod on it. If your build can not handle reflect, you need to be able to hit only the other ones, which is possible on some builds, but can be difficult if using AOE, projectile behaviors etc. Any of the other 3 are fine. One of them has some blue colouring on her, so people sometimes use that one to attack, since it is easy to identify as being not the mirror version.

There are some other challenges in the fight. She has curse reflect, so curses you may be applying to her can also be applying to you, which in the case of flammability, elemental weakness and some other ones, could be making you weaker for the fight, if you can not handle the cures. Some of her abilities are dangerous as well. The flame blast and her other mechanics do a lot of damage but are fairly avoidable once you learn the mechanics. If your build is close to beating Maven, it can probably do this fight, so long as it counters the things that are being mentioned in this thread. It is not an extremely difficult fight, but it can be very though if you don't know how it works, and though to learn by trial.