User blog comment:Hamengeri/Outrageous Runic Blade (Custom Item)/@comment-1330314-20130824211440

Thing is, an item with this kind of passive removes mana costs entirely, and coupled with the defensive stats would be a must-be rush in mid lane, even if the AS is wasted on the caster. On top champs, too, this'd give way too much sustain in lane and, coupled with lifesteal, could allow mana-based champs to last forever.

The other problem is the ultra-synergy with : the latter's meant to deplete your mana for extra damage, but buying this item removes the cost to Muramana entirely, since you're bound to end up regaining as much mana as you're spending.