Sky Attack now has a 30% chance of causing the target to flinch. It also now has an increased critical hit ratio.
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According to Bulbapedia, both Super Luck and Sky Attack add 1 stage of Critical Hit chance. This means using both you would have a +2 Critical Hit stage. In Generation 8 that gives you a 50% chance to have a Critical Hit with Sky Attack. If you add a Scope Lens, that adds another stage, giving you a guaranteed Critical Hit every time you use Sky Attack.
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Hope I helped. If I am using the wrong generation, let me know and I will fix the odds.