Spider-man injects himself on purpose with some sort of radioactive material, thereby preventing Morlun from sucking out his essence. This is the first instance that Inheritors like Morlun are revealed to be weak against anything radioactive. This same weakness will be used by the various Spider-men from different universes to defeat the Inheritors during the Spiderverse storyline.
From – The Amazing Spider-Man Vol. 2 #35
Then I presume he spared Morlun’s life?
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