To explain it better what I did.
I took the CoordProjectileEffect class and edited to non target, where instead of having a mob targeted it cast a projectile to the mouse position. When casted, it emits a Game Object (Particle Object) where I have it moving until the mouse position and on this game object I have the physics, where if it hits the target do the hit effect.
From client side it works. But sometimes, it detects the hit with my class on client side but not on server side because from when the spell was casted and until the hit, the target destination moved.
From what you said I had an idea. on my side, instead of just emitting a hit game object, that game object could have the skill area aoe. instead of just being a VFX GO it could be a Coord Effect. right?
About the isometric and 3d is different, we need to think more in 2D rather on 3D. the hit box works differently.
I don't know if i can share here images but I'll post a link. https://imgur.com/epYe7CR
From that image for example, the pink monster, has to get hit by a large hit box, not just comparing with the root position.
we need to think like the creature is printed on the ground, changing the areas of hit coord on X and Z.
But I will try that idea you gave me and let you know