Frankenstein Lighting keeps Sieg alive

However, while Siegfried’s body could withstand the dragon blood within it, Sieg’s body can’t. That is reason that the spots on Sieg’s hand where the Command Spells disappeared from turned black. Even after he used them all up, power Sieg obtained from Frankenstein’s “Blasted Tree: Lightning Branch of Crucifixion” managed to barely maintain his human form, but that too was used up when Sieg used this Noble Phantasm at the end.