Surtur has a giant flame sword and with it he can slash away at Lucifer’s health. Lucifer may be a being of magic powers who cannot lose to many opponents, but in the end he’s not at Surtur’s level. Surtur is the ultimate being of fire and cannot be stopped. Surtur wins.
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Lucifer can warp reality & is omnipotent….he could snap his fingers & erase Sultur from existence….lol!
You can’t snap someone out of existence if they don’t want to be snapped though