How do you ensure you don't miss important edge cases while testing large, complex tickets on the last day of the sprint?

When faced with testing large, complex tickets at the last minute, it’s easy to miss important edge cases, which can lead to undetected issues. How do you make sure you thoroughly cover all possible scenarios, including edge cases, given the limited time? What strategies or tools do you use to track these cases, and how do you prioritize the most critical ones to ensure comprehensive testing under pressure?