Elden Ring Nightreign Everdark Sovereign explained

What are the Elden Ring Nightreign Everdark Sovereign events? As if Nightreign wasn't difficult enough, the developers have added a new mechanic to the game that strengthens specific Night Lords at the end of each expedition. The rewards for taking down these enemies can drastically change your builds, so it's definitely worth pursuing to become significantly stronger.
These supercharged Elden Ring Nightreign bosses appear on a weekly schedule; if you want to take them all down, you're going to need to do it sooner rather than later. The Elden Ring Nightreign events in the co-op game are currently available for a limited time, but FromSoftware has said they will be made permanent at a later date.
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Elden Ring Nightreign adds new, seriously hard bosses, but not for long