Thật ra thì ...
The first slash has a ministun.
The cooldown between slashes is 0.4 seconds.
The slashes aren't real attacks themselves. Omnislash works by teleporting Yurnero to a certain enemy unit around every 0.4 seconds, playing Yurnero's attack animation (the animation of attack, not Attack Animation), and dealing the slash damage by trigger.
Each slash deals
150 - 250 Normal Hero damage which is reduced by the target's Armor and is blocked by Stout Shield, Vanguard and Kraken Shell, but not Magic Immunity.
Linken's Sphere blocks the ministun on the first slash. The damage from the first slash would still be dealt and the other slashes would still occur.
During an Omnislash period, Yurnero is Invulnerable and Unselectable (if you selected him, a trigger would make you instantly unselect him).
With enough IAS, Yurnero can 'extra' attack while Omnislashing. If the attack cooldown is short enough so that right before Yurnero is teleported to another unit, he can finish an attack, then this will count as an extra attack (dealing Yurnero's true damage, and applying Orb Effects, Bash and Critical Strike if any). Here is a graph that shows how many extra attacks Yurnero can get in, with a certain IAS:
Đừng nên nói phủ đầu kiểu như "tôi đã từng làm trigger cho omnislash blah blah ..."