Shyvana is a great example of a balanced manaless champion. She has one major problem though.
She can only use her dash/gap closer ONCE Her only CC is a minor minor knockback She doesn't have any sustain built into her kit She doesn't have reliable click and point poke She's meele
For reference, here's all the manaless champions http://leagueoflegends.wikia.com/wiki/Manaless
There is still a major gameplay problem with Shyvana though. A good portion of her damage is magic when she builds Tanky AD.
You have to itemize Armor. She is going to get BRK and her Q hurts. You have to itemize MR. Her W, E, and R, all do magic damage. Which means that you have to itemize Health. Except she does 2% max health dmg.
If you change the damage on her W and R to physical damage, then she would be a lot healthier because you can actually itemize against her.