Compicated Spell ( or not ?)

I Want to create a passive spell that would work like Critical ( in percentages each time the user attacks ) when its activated it will appear as a buff on the effected unit. the unit will be disabled in a manner that it cannot move. but it will be able to attack
another tricky thing is that it will last forever, unless someone dispells it. something like unlimited Entangle but able to attack.
please help me, id rather do it without triggers. any ideas ?

You might be able to use the Orb of Lightning as a base ability (this will not work as a Hero ability with multiple levels) This accomplishes the % chance of the effect.

As for disabling, spells currently have a limit of 300 seconds, so without triggers, you can't have a buff that lasts "forever". (Of course, I strongly recommend you use triggers to get the effect exactly how you want it).

You could make the spell that is cast to be Ensnare. You'd have to increase the attack range of ensnared units (it's one of the editable fields), with a 300 second duration. This won't exactly work how you want it, though... There are many better ways using triggers...