Surprisingly Quick Reflexes

You’re quick, for a Tortle. You also have a shell, as a Tortle. Those two things combined grant you the following benefit:

As a reaction to being targeted by an attack, you retreat into your shell until the end of the current turn. When you do so, you gain a +4 bonus to your AC, potentially causing the original attack to miss. You are then considered prone until the end of the current turn. You can use this reaction a number of times per long rest equal to your Constitution modifier (minimum 1).