I haven't given it much thought yet, but I think I'd like his level 10 to have different Mage buffs to choose from. Stuff like Arcane Power, Presence of Mind, Time Warp, Combustion, etc. Jaina already has Icy Veins, but all the rest are still available (Kael'thas has a storm talent called Presence of Mind but it has very little to do with the actual spell from WoW, it's just a vague reference to it being commonly cast before Pyroblast in the past). One nice thing about them being castable...

Finally... He is here... the prophecy is true...

Lol, hard for me to call it more thought out when I don't bother with numbers or talent trees, but thanks! Yeah, having a cooldown after casting a spell could be a way of setting a limit to his combo potential with his own kit too, if any in particular prove problematic. Hm, I didn't really think of any specific talents, but I guess they could still be similar to those of other heroes. Actives could be a bit weird and might be best to avoid, and he would probably have more talents that...

I added some overall thoughts on cooldowns to the new "balance considerations" section. I do think there should likely be at least one global cooldown somewhere, but I think having it between QWE casts would be the clunkiest option. I'd prefer stuff like them going on a cooldown after you switch spells. That way conjuring still feels responsive and fluid, while also forcing you to stick to your choice for a few seconds (punishing Khadgar's mistakes if he brings up the wrong spell).

Yeah, the elements being conjured should definitely have some sort of visual, and personally I'd say it should be visible to everyone, it wouldn't be any more "cluttering" than Kael'thas' Verdant Spheres. As for reseting, I think it's another thing that worked out very well in Gauntlet. After conjuring an element, you have something like 1 second to conjure the next one, otherwise they reset to nothing. Conjuring two in a row consumes them and "equips" their...

A short global cooldown could be necessary for balance reasons. He doesn't have any particularly crazy combos on his own, but maybe someone with high enough APM could be a monster if there were no cooldowns whatsoever to switching spells. Cooldown display is interesting to think about in this case! I pretty much just imagined picking Merlin straight from Gauntlet and dropping him in HotS exactly as he is, as I found his design there to work incredibly well, but I see why it could be...