I think super smash and arena game is the same and those votes should be merged ;P
For the super-smash arena game i would suggest you take alot of inspiration from the map Warlock since it's already so successfull and awesome!

Atleast the part where you design ur own fighter from scratch and upgrade the spells you want to concentrate on gradually is something we should definitely use!
And that you can choose between 3-6 different models from start and they all got different, but similar, essential spells that they start with.
Fireball and scourge like they use in warlock are great for this purpose since they are the most basic of their type, fireball which is a straight forward click'n'shoot spell and scourge which is ur basic close-range AoE "stomp".
They could ofcourse have different effects like slow, stun, dps etc. depending on which model you choose to play with, the spells you choose to buy should complement the essential spells tied to the hero model you choose to play with which will add an aspect of strategy
One way to go with it which would differentiate it from Warlock(and add even more strategy) is to choose elemental models and have their spells be divided into different elements like water, ground, lightning, fire, darkness etc. and have like ground>darkness>lightning>water>fire>ground, so if f.ex. a ground spell gets hit by a fire spell the ground spell would disappear and the fire spell would keep going.
To really make this flow well the essential spells tied to the different models and the different elemental spells would really have to complement eachother in a way that picking a certain model would automatically lead you to go for one type of elemental spells(f.ex. by having the different models slightly buff it's corresponding spells, and ofc make the essential and corresponding elemental spells fit eachother), but then ur opponent could counter with the opposite elemental spell and force you to change ur planned build and miss out on great combos that ur essential spells could get with the corresponding elemental spells.
Important that the competing players don't see what model eachother choose until they start buying spells(could be solved by not moving on to the spell shop until everyone has chosen a model, like in Warlock ;P)
That means most likely all spells would be used and ppl would rarely play with the same builds cause they would get countered if they do

Balancing would be a nightmare ofcourse, but i would dedicate alot of time to helping out with this and i'm guessing alot of ppl from the warlock community would also help out
Another thing that could make this very different from warlock would be to add a height/depth aspect, since warlock is practically 2D it don't have any high/low-ground which could make it very very different and open up for more varied spells and effects
Check the different arenas from
Mad Balls Arena, could give some ideas
Also i could make like atleast 20 strong concepts from using the
CTE(custom terrain editor) made for Warlock
But an important thing to keep from warlock would be that you don't click on your opponent to cast spells, but use your aiming and dodging skills instead
Really really hope you choose to go for this type of game, it could be fucking awesome! ;D
If you feel it seems a little limited we could ofcourse have several modes like a boss-mode and take aspects from
Impossible Bosses
There it's all about teamwork instead of fighting against eachother, would ofcourse have to add a healer-class like priest in IB for this mode, either that or trade one of the essential spells on each model for a healing one
I'm trying to limit myself and just come with the basic ideas first hehe but i got much more in my arsenal! This game could be soooooo awesome!!
So please make the right choice and vote for a super smash arena game, it's instant success! hehe
Edit:
Here you can see the last attempt to make a standalone
I guess it got abandoned because they were expecting to get financial sponsoring, but might have jumped the gun a little(imo) and didn't get it, also i think the team that worked on it was only consisting of 2 or 3 ppl so it probably got a little overwhelming for them to do it without payment since they were expecting to get sponsored and all, i think if they did a little more work so we could atleast try an alpha version we'd provide enough hints and tips to motivate them to keep working, but they gave up too quick i'm afraid, lets not make the same mistake here! ;D
On a sidenote, hotkeys for the different spells should be designed like they are in warlock, easiest way to have many hotkeys and still keep control of which is which, if one more hotkey is needed i think Space could be easily added
