Since Dark Sera has been ninja buffed with the orb machine gun. Clearing it is harder now. It becomes a race against time before she uses it alongside the dragon flame breath attack.

So far the most success I've had is to bring Anut. I don't remember if the physical or magical immunities were removal before but now you can. Your solo hero clearer should either have HUGE burst damage or stun having both makes the match trivial.

I've tried 5 runs with my 6* 3 Archon and she did great 100% clear but I have tMR on her so I'm not sure if she's 100% viable or not. If you have a well geared Archon, you can probably burst her down before she even gets near you.

When using Kriemhild it gets riskier as you can get screwed by block generation harder. I've tried a lot more runs with her compared to Archon maybe about 20 or so. My Kriem has level 4 Revolution Hammer and I equipped her with an Ice Hammer ( Armor, Damage Reduction, Lifesteal) for testing. Success rate is about 70% at best with some close calls. You need to manage your Anut timings. In this setup it's better to actually save the uses for fire breath and when she gets the attack buff. I've managed to live ONCE through the orb spam just because of removing the attack buff.

Last hero I tried is Korin. I don't have any good weapon for her so I opted for a Sister Staff with resist penetration and life steal. I just went with this once since I wasn't confident that I'll pull it off. Fight went too long for comfort luckily Sera didn't do the orb spam.