Encouraging:
* You got this!
* You can handle it!
* Go get 'em!
* Don't give up!
* You're a rockstar!
* You're awesome!
* You've got this in the bag!
* You're killing it!
More informal:
* You're good!
* You can do it, bro!
* No sweat!
* Piece of cake!
* Easy peasy!
* You got this, dude!
Sarcastic:
* Sure, you can...
* Yeah, right...
* Good luck with that!
Choice will depend on:
* Relationship with the person
* Situation
* Desired tone
Let me know if you want to know the most suitable slang for a specific situation! 😊