User blog comment:AP Sejuani/Mira, the Corpse Collector/@comment-26044269-20150127130757

Although I'm not totally against the idea of an ability which allows Mira to 'steal' her opponenet's abilities, I am deeply persuaded that such an ability is one of those curious things that only looks pretty on paper.

One of, and the most prominent reason why I am persuaded to think this way is because of the lack of details you've listed on the actual ability. Because as of now it is unlisted whether or not Mira can also 'steal' the opponenet's resource bar.

Say, if Mira was to 'Reave' Shen, a champion who uses Energy and not Mana for his basic abilities, would Mira be able to cast the 'stolen' abilities even though she does not have any energy? Or if Mira were to 'Reave' Rengar, a champion whose resource bar tracks a gameplay mechanic rather than an actual limitation of some sort (Energy, Mana, etc), would Mira be able to gain Ferocity stacks and gain access to Rengar's empowered abilities (which of course is what makes Rengar a truely unique champion)?

Plus, if we are to keep in mind that basic abilities and their respective Mana (or Energy, w/e) costs are created with the subject champion's overall design and his/her base stats closely in mind, it should be fairly obvious that an ability which allows one to 'steal' someone else's basic abilties should not even exist in the first place because of the sheer amount of counterintuitivity it brings with it.

So tl;dr, either scrap the ultimate and rework a new one since it's basically only there for its thematic value anyway, or make a detailed list of how Mira would react upon 'Reaving' different types of enemies (and try to make them reasonable).

+1 for ME!ME!ME! btw