Custom Berserk

Increases damage, and attackspeed by 100%. The caster will lose 5% of health every 5 seconds. Lasts 30 seconds.

I've used berserk as a base with attack speed bonus as 100% with a duration of 30seconds, but i dont know how to do the 100% gain/loss in GUI.

Can't just do it via a trigger as you want.. But, just make a dummy upgrade that boosts attack speed which that unit has, when the unit casts it, set the upgrade to level 1.. when it over, set it to 0 again.

But whats the problem with using the ability to do it?

Because theres no spell that increases AS as well as damage.
Is there even a spell that reduces your life?

Yes, there is.

Unholy frenzy deals a set amount of damage every second; and it increases your attack speed.

Ok thanks, never noticed that unholy frenzy drained hp.