Thanks for the advice.
There still seems like a lot of stuff to work on. Stats seem OK, though a little small, and you haven't mentioned how progression will work. Finishers are rather generic, so there should be specific finishers characters could have that alter finisher strength in certain conditions, or possibly "finishers" that are harder to kill the enemy with, but provide a buff/debuff against them that turns the remaining battle in your favor. Weapons system could work, but the positioning part of it should account for more; shape/nature of the area, target's ability to react and move away, and maybe how positioning within the area affects damage, etc.
Yep. It's not a fully fleshed-out idea yet.
Regarding stats, I wanted a small number of base stats because the more I add, the more difficult it becomes to make each stat point worth the same. The idea is that each stat should contribute to a damage advantage in some way, either by protecting you against damage, or by granting you ways to deal damage. Since Agility becomes the most versatile (it can do both), the other two stats grant other advantages to make up for a lack of versatility.
There are other minor stats I was thinking of, such as Precognition (gives you a chance to predict NPC attacks), Evasiveness (creates an area of uncertainty as to where you'll be), Fortitude (chance to resist enemy positioning-altering abilities), and perhaps Reflex (Determines what bonus you get to blocking abilities that you predict). You'd get those through either spending a different kind of points than the primary stats, or through special artifact items.
I was thinking of different kinds of finishers having to do with the game setting, such as a finisher that separates the soul from the body (lets you still fight on as a soul, but only through magical attacks) and a kind of death blow that causes lasting harm to the body itself, but doesn't have an effect on soul attributes.
Abilities can be modified finishers, so there's room in the mechanics for something different there.
As for weapons, I was thinking of having different mechanics for projectiles, thrown objects, sweeping blade attacks, etc. However, anything with an area-of-effect and special shapes of the area would technically count as an ability in the current system, and the nature of the area would be defined in the ability description. For example: A 120° sweep with a range of 2 units, dealing damage to the first target hit.
That'd make something like a grenade launcher an ability instead, which I guess is kind of unintuitive, but most weapons wouldn't have that kind of sweep.
...Maybe add some default abilities like a wide slash, a kick, or a bash that sends the enemy flying.
Speaking of which, that's the biggest problem; Positioning. It is a mathematical nightmare. For players moving around a stationary point, it's OK, since you often have to recalculate distance between any 2 points to locate all sorts of things. For players moving around Eachother, there's so many ways their relation to other players has to be recalculated, and numbers'll get so specific that you have to round at some point. Don't forget whether you're measuring tangent velocity with degrees or distance per second. Then there's trying to convey it all clearly to players.
Positioning was something I thought would be a problem as well. I think the easiest way to resolve it though would be to make a map. Simply have a grid and draw an arrow.
A grid would mostly restrict players to a certain number of axes of movement, but I think we can get around that. Direct speed can be the longer arrow and tangential speed is the dotted line:
Of course there are edge cases where you get less mileage out of your direct speed than you'd like. Take this for example:
...where Tangent speed and Direct speed are equal. In that case, we could just say that in melee, you can consume any kind of speed, since you're colliding with your enemy anyway.
Environments probably need to be represented better. An area like a graveyard with lots of obstacles, for example, could be used against enemies by simply using a displacement ability.