Bladestorm - how to detect?

If i wan to detect a unit fininshes using bladestorm, what event should i use? and also what is the diff between starting the effect of an ability and begin casting an ability?

begin casting is before mana is spent... in this event you can stop the spell
begins effect is actual effect... mana is spent even when you stop the caster.
for bladestorm use begins effect

He actually asked for an event for when Bladestorm is finished.

There is no such event, but what I would do is, simply register when it starts, use game time (polled) wait for the duration of the spell, and then check if the Hero is alive and unpaused and execute your actions.

(Unless, Bladestorm can be disabled, but I don't think it can, correct me if I am wrong.)

I think Bladestorm uses a buff called Bladestorm (Caster) eventually make the wait a little shorter than the duration of the spell and check if the Hero has that buff, and if he has it, execute your actions.

Blade Storm Cannot be dispelled because the hero experiences magic immunity during it.

I believe you can be bashed while bladestorming, i'm not sure though. I think you might be able to be ensnared as well (i wouldn't put it past blizzard making ensnare able to counter another ultimate - it already counters all the channeling ones) - if you can be ensnared I don't think it cancels it, just stops the movement.

Edit: I tried it out, Bash deals the bonus damage to the blademaster, but doesn't stun. Ensnare CAN be used on bladestorm, it stops movement but doesnt stop bladestorm

Well... bash and critical strike works on dryads so... magic immunity works on specific abilities

I guess blade.dks solution would be the best here.

Solved it by using the ideas u guys gave.
hmm, i am stuck at detecting a "line range", my spell is based on carrior swarm, but the damage is base on the int*hero level. I did a trigger, but the problem is i cant get to order the dummy to damage the unit in a line. I tried "from caster to target point of ability being cast" but it wun work when a player selects a point which is lesser than the original range. 1000.

If i didn't understand you wrong, try creating another dummy unit at the range of 1000. Order the dummy unit that damage to attack picked unit inside the range from caster to another dummy. (Correct me if i am wrong) I think you also need to create a unitgroup var.