Do any champs build Manamune anymore?

Ezreal. That's about it. Malz used to have it in an AD off build, but it got nuked with his micro-rework.

Jayce on occasion.

I like it on fighters and assassins to solve mana problems but then you run into adcs and are too squishy if you dont have every item into defense in some way. ad at least 3 in armor same thing with mages if you dont have 4 dipping into defense and 3 into magic resist

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My Nasus build uses it (but my build while perfectly serviceable (and in my opinion better than meta), isn't meta).