I decided that I wanted to train a nice Fearow to have in my P.C. box in Pokemon Moon. Fearow's main ability is Keen Eye which makes it unable to have it's accuracy reduced and can ignore evasion boosts. It's hidden ability is Sniper which makes crits deal 225% damage instead of 150%. Obviously Sniper blows Keen Eye out of the water. I'm not too worried about Flash and Double Team.

How do you get a hidden ability? You have to get it from S.O.S. chains. S.O.S. chain battles have these traits.

Defeated Pokémon - 5+ - 1 IV of 31 Guaranteed
Defeated Pokémon - 10+ - 5% Chance of Hidden Ability
Defeated Pokémon - 10+ - 2 IVs of 31 Guaranteed
Defeated Pokémon - 20+ - 10% Chance of Hidden Ability
Defeated Pokémon - 20+ - 3 IVs of 31 Guaranteed
Defeated Pokémon - 30+ - 30% Chance of Hidden Ability
Defeated Pokémon - 30+ - 4 IVs of 31 Guaranteed
Defeated Pokémon - 70+ - Shiny Pokémon Chance increased by 3 giving a 1 in 1024 chance without Shiny Charm and 1 in 683 chance with Shiny Charm.

Your best odds of catching a hidden ability pokemon involve killing 30 Spearows first and then catching the 31st. But this only yields a 30% chance of the pokemon having it's hidden ability.

If I want to catchs Spearows with Sniper, I will have to sort through an average of 98 Spearows between each Sniper Spearow. I guess you get the bonus of that Sniper Spearow having 4 perfect I.V's, but it's still an absurd amount of Spearows to sort through.

Why does Game Freak want me to kill 98 Spearows?