In Elden Ring, if you get branded by the Frenzied Flame, you are destined for the bad ending(Lord of Frenzied Flame ending). But there is a way to subdue the effect of Frenzied Flame. For that, you will need Miquella’s Needle, which you will get by completing Millicent’s questline.
once you have Miquella’s Needle, go to the Crumbling Farum Azula and make your way to the Beside the Great Bridge Site of grace as shown below. Then take the elevator down.
After coming out from the elevator, climb down the stairs, move ahead and go out from the western side of the building. Stand on the edge and jump down on the rocks to reach the floating structure as shown in the picture below. There you will get the option to “Lie Down” as shown in the second picture below. On lying down, you will reach Dragonlord Placidusax secret boss chamber.
Use the Miquella’s Needle in Dragonlord Placidusax‘s chamber. You don’t need to defeat him, just open your inventory and use the needle to tame the fame of frenzy. Now you can finish the game normally and won’t get the bad ending.