So I checked out Ketheric Torm after visiting Nightsong.
This scroll is capable of bugging the game, at the moment when the castscene should be played, nothing happens, but the petrification passes and you can continue to beat them.
As a result, Ketheric Torm continues to fight with 0 HP, and it is impossible to kill him on the roof of the towers, so as not to crash the game
You only have to lower his HP to 40 up there for another cutscene, since you have fight him again 2 more times.
When his HP drops below 40, but he is in the golden statue state, the castscene does not trigger. Instead, he is cured of this condition and continues the fight, but it is impossible to kill him even with 0 hp because he is scripted and cannot die on the roof
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I also checked the possibility of turning Gortash into a golden statue.
This is possible, but it will not interfere with the coronation scene. If he turns into a statue after this, everyone becomes hostile.
Perhaps we can try "higher invisibility" rather than just regular invisibility to prevent the castscene from triggering.
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My next experiment is to prevent the castscene with Jergal, at the moment of Dark Urge's redemption, what will happen if Jergal is in the form of a golden statue
