Good to see my Cursor put to good use. I've tested it, and it seems mainly bugless. Can't say much about the balance, I've never been a good ladder player.
The casters seemed strange to me. The Navi Priest seems rather useless to me. His low mana pool makes him not really useful for healing (He's empty after less than half a fight), his second ability is explode, which is an overall useless ability (No one spends that much resources just to waste them for a area dispell.) And the Aura isn't stacking and can be optained easier from merc camps, where the unit has also more than just the Aura. Since there are critters of the same shape on the map, the Navi Priest might be useful for scouting, but is placed to high in the tech tree for that.
On the other hand, we have the Naga Siren, which seems a good caster to me. And she can turn into another Caster, Naga Summoner, with completely different spells that nonetheless use the same upgrades. Two birds with one stone.
My suggestion: Remove the Navi Priest or make him a half-caster like the Spell Thief or the Faerie Dragon (and choose a different model please). Either separate Siren and Summoner or make them use their own Upgrades.
And the Tooltips of the Poison Thing Hero (Misha's Naga Warlord) say "Nature Mage" you might want to change that. Misha's model has a small flaw, the Shell parts of the hero are unshaded and unfogged, making them appear too bright during the night. You'll find a fixed version attached (I've got permission)