Perhaps this has been suggested before but it feels as if the Muramana's toggle effect may be a little difficult to read sometimes. Perhaps if the item icon had a sparkly animation effect when active it would be better? Since there wasn't any toggled based equipment before season three perhaps the tech isn't in place but you could probably extend this idea to potions and any other potential toggle based equipment. Or a more radical approach would be to somehow highlight the mana bar when Muramana is on.

Perhaps something like when Vayne's W is active?