Here’s a list of 300 idioms ranging from informal to formal. I've categorized them to help you see the progression from informal language to more formal expressions.
### Informal Idioms
1. Bite the bullet
2. Break a leg
3. Cut to the chase
4. Hit the sack
5. Keep your chin up
6. Let the cat out of the bag
7. Pulling your leg
8. Shoot the breeze
9. Spill the beans
10. Under the weather
11. Kick the bucket
12. The ball is in your court
13.