The Necrotic Grip exotic isn’t restoring melee energy when a corrupted combatant dies, which is half of its perk.
There also seems to be an issue where the corruption doesn’t spread when a combatant is corrupted by using Thorne and they die from corruption. I have to kill them with Thorne for it to spread.
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It's already one of the strongest exotics in the game, it doesn't need extra melee energy involved.