This is the guy we are suppose to hate!!! 
I'm on my way to taking his crown
Really though all jokes aside it takes a perfect kind of setup for me to kill an HQ because if someone does defend their HQ it's gonna be a wasted trip.
1. City must be under 50% but the closer to zero more likely I'll take a stab at it.
2. Within an hours distance from where I launch from.
3. Easy terrain as I never attack an HQ flying above 10k.
4. No bases to give it away what I'm doing.
5. Does not help the other opposing country. If I don't think it will help my country such as deterring an offensive or keeping them blind while the horde is rolling I won't go. This one kills it 90% of the time. I really don't like to JUST kill the HQ it's too high risk and I hate wasting time.
