Destiny allow us to upgrade the mythoclast to 331, the same as all other exotics. This gun took many hours to receive we should at least be allowed to upgrade it to the same attack damage as the rest of the weapons post dlc.
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I'd say leave it as is. Its already a strong weapon, and its also a weapon of the past, like Fatebringer and Confluence, they shouldnt be upgraded. But thats just me.