u/Artorias42

I have a unit at a battlefield and one hidden unit. The opponent attacks with a Kha'zix Mutating Horror and the "When I attack" trigger goes on the chain because only 1 unit is present on my side. As a reaction to this ability I play my hidden unit. Does Kha'zix ability resolve or does it fizzle because now 2 units are present?

According to a facebook post Kha'zix does nevertheless get the +2 might. But I dont understand why because the condition is not true anymore when the ability tries to resolve.