Double Attack?

K,quick question, How do you make a double attack. hopefully you know what a double attack is but if you don't (hero attacks two times),one imedieatly after the other (realy fast)

That is usually accomplished by creating a dummy unit with terminal attack speed so that the second attack happens at exactly the same time. That's if you are using a ranged attack (2 missiles created). But you want the hero to look like it's attacking twice, correct? So I would trigger it this way: When the hero attacks or casts a spell (you didn't specify), a basic haste ability is added and quickly removed after the interval of two fast attacks has passed. Try to be more precise the next time you ask a question, it helps everyone figure out what you want faster.

If you don't mind the ability being an orb effect, you could use Orb of Lightning/Slow with the ability to be cast set to Searing Arrows, and change the proc chance. It doesn't have to be triggered that way.

All the issues with orb effects and Orb of Lightning/Slow apply to the new ability, though - for example, only targeted attacks trigger it.

And orderering units with the artillery attack type to Attack Ground will crash the game.

Orb of Lightning + Searing Arrows is how Gemini Attack from DotA's Nerub Weaver works.