Play God
Definition 1 of 1
Pro Tip 1/3Moral Implications
The phrase often implies moral judgment of using excessive power or overstepping ethical boundaries. 
When the CEO fired half the staff on a whim, employees accused him of playing God.
Pro Tip 2/3Used Critically
It's commonly used in a critical way to show disapproval of someone's actions or decisions. 
You can't just decide who gets to stay on the team; you're not playing God here.
Pro Tip 3/3Idiomatic Nuance
The phrase can be used metaphorically to discuss actions that drastically alter natural or expected courses. 
He tried to play God by controlling his children's every decision.