Oh man death blight builds can be pretty annoying to deal with but i've got some solid counters that'll help you out. First thing you wanna do is stock up on rejuvenating boluses, they're honestly a lifesaver and you can craft them with some dewkissed herba and crystal cave moss. I always keep a few handy just in case.

Those prince of death talismans are super useful too, especially the cyst version since it gives you way more resistance. I usually pair that with some high vitality armor like lusat's set, makes a huge difference when someone tries to stack that death effect on you.

Something i learned the hard way is to watch out for that eclipse shotel, especially when they try to combo it with fire's deadly sin. As soon as you see that red-black glow, just create some distance and maybe throw some lightning their way. The whole death blight thing needs them to stay close so keeping your distance is actually pretty effective.

One thing that's helped me a ton is having order healing ready to go, it completely wipes the death buildup and catches a lot of people off guard. Just remember if you're in a tight spot and see someone breaking out fia's mist, don't try to tough it out - use quickstep to get outta there fast. Better to reset the fight than get caught in their setup, you know what i mean?

The main thing is staying cool and not letting them pressure you into their game. Once you've got these counters ready its actually pretty manageable, since they need time to build up that death effect. Just keep moving, punish when they try to buff, and you'll be fine!