Damn, so the idea pretty much falls under awesome but impractical.
I'd say it roughly falls in line with the other two, being just as strong as them, but in other ways.
Having unlimited mana means you can spam as many 10th Tier Magic spells with as much metamagic enhancements as you wish. Any battle between two spellcasters is, frankly, just a question of who runs out of mana first: What matters is casting efficiently, dealing damage without losing more MP than your opponent, or forcing your opponent to lose MP on useless spell, or going with a "go-all-out" strategy where you pour all mana into offense to overwhelm your foe at the cost of losing mana and therefore opening yourself up if the gamble doesn't win.
The entire "unlimited mana" skill basically puts a lid on that, since you can cast as much as you want without having to fear repercussions. In other words, it forces your opponent on the defense and lets you get in a bunch of free hits. This ensures total victory in most mage-vs-mage combat, unless the enemy has other trump cards present.
However, the time limit of two minutes is rather rough and forces you to fight quickly. If multiple opponents are present, you might not make it.
On another hand, the ability to turn into five different forms grants a small set of versatile trump card-like abilities to call upon to deal with varying, but powerful threats, not to mention the mere shock value of them. Each form is easily capable of taking out a Boss-level opponent, so the results are promising, too.
