Warframe

The hit boxes are very janky on this boss. My recommended build is Rauta Primary and a Stropha modded for gas heavy attacks. You should be able to 1-2 shot each phase with that. You want to be able to get your damage in before damage attenuation kicks in.

If this is more for the "secret boss", I really don't like that fight, it feels like it was designed to make meta a requirement. Heavy slam attacks are still useful for this version of the boss, and landing on top of the tank should keep you out of the nullifying corrosive sludge. I still dislike that it mostly revolves around abusing invulnerability to defeat a boss.

And I guess for anyone that doesn't know about that boss yet,

spoiler

Defeating it gives your landing craft a turret Sumdali, and defeating it solo with a Hex warframe will give you a glyph.

Apparently there are another 6 warframes which will get a glyph for defeating the 60 eyes boss solo.

Jade's AC-130 mode helps a lot. Funnily enough, she can get staggered in the air when the tank first shows up, but after that she's fine.

Its not an overly hard boss but its exmplery of how rotten warframes core mechanics are at this point. Especially in the apex version its just cheese the boss before it cheeses you.

Personally I think its down to how abundant healing has become, We can instant heal at will so the only damage thats meaingful is oneshots, and when that's the case it invalidates all the survivability mechanics that aren't one one shot resistant in turn, and the only worthwhile defence for enemies is either weird damage calculations or disabling half the mechanics we play the game for in the first place. Healing is out of control and player damage is out of control and its eating away at the core gameplay loop.

I actually love it, it doesn't feel like a slog but I guess I am cheesing it a bit. It's much more fun than the Murmur boss since instead of being a damage sponge with tons of attenuation, here you actually have to move around the area, aim at weakspots, grab the RPG from other units, CC the healers in the 2nd phase, etc.... It's dynamic and requires skill over fighting dmg attenuation IMHO.

And in the end, what's wrong with cheese? It's called bringing the right tool for the right job and being prepared/adaptable, whether that's Unairu/PSF, Incarnon weapons, armor strip, rolling guard or w/e else you might need.

edit: I have been doing the secret apex H-09 fight for the accolade glyphs and honestly it's one of the more satisfying accomplishments in recent memory. Not only is the fight pretty fun and maybe even too easy with the correct weapons, just the feeling of seeing these really pretty glyphs as my loadout icons or backroom decorations is 10/10.

If I can endure the much longer 60 eyes setup and fight I should probably go for that one too...

I really haven't found it all that bad, the key was staying mobile. I beat the Steel Path version while using Mesa with no stagger immunity mods at all by bullet jumping around and aim gliding, most of it's attacks can't do anything to you when you're in the air. It also goes down pretty fast when you shoot it's weak points, and doesn't appear to have attenuation when doing so (or at least it's not noticeable). I'll take more bosses like this guy and Exploiter Orb any day over more attenuation/damage sponge bosses like the Archons or the Murmur boss.

Primed Surefooted is a thing. It is pretty valuable already, on this boss it negates all staggers.

I honestly enjoyed the tank! I do agree with you that the second phase is far more ground AoE and stagger-centric than what we've seen before, but I started Aim Gliding around the thing and barely get damaged now (boosting Parkour Speed helps a lot, I have a single Tauforged Yellow Archon Shard slotted for +22.5%). That should keep you clear of any ground-based shenanigans.

As for the big physical attacks, I try to Bullet Jump straight up whenever I see it rearing, then hover with Aim Glide while it does its thing. It sucks a lot that they capped the ceiling to the crater's lip, being boxed in like that does tend to make things a bit... cramped for my taste.

I also found it vital to manage those tendrils it pokes out of the ground with priority, as those can DoT you down pretty fast.

Other than that, it's down to popping the weak points as fast as possible. I've had runs in Pub where neither I nor the tank got to do much, because my squadmates brought it down in under a minute (not counting the healing phase).

To be honest, I have more trouble with its first phase, mainly with the aerial adds. It's like my brain can't fit them into its action plan. Still find it a good challenge, though, it's just that it hasn't clicked yet.