Actually, they do stack, but not adding up like that.
The general formula for most of the stacking problem in W3 is like:
A = 1 - (1-B)(1-C)(1-D)... and so on, with A is the final value; B, C, D is the value of each of the component.
So in your case, if u add the -25% magic resistant to ur hero...
Erm, I just figured out how to do the chain thingy just now. Just make a few arrays to create n dummies for n matching targets in the area around the caster, then its fine. But well, I still have trouble with the damage counter -.-'! The event response - damage taken, atked unit, atking unit...
Im currently new to WE, so I only know how to work with GUI atm. And im working on my new hero idea, which has an ultimate that kinda work like Dream Coil.
The spell is like: the hero will take 1.5s channeling to cast the spell, after that, it will create a chain to enemies hero within 600...