When you reach zero hit points, instead of going unconscious immediately, you can choose to enter a Last Stand.

• You immediately lose concentration on any spell that is up, and you can not cast any new spells.
• If you are hit again, you automatically fail one death saving throw, (two on a critical hit,) and you must succeed on a constitution save of 10 or half the damage taken, which ever is higher, or you immediately go unconscious.
• While at zero hit points, you have a speed of zero.
• You have advantage on any attacks you make while you have zero hit points, and all hits are treated as critical hits.
• If you end of your next turn with zero hit points, you fall unconscious and automatically fail one death saving throw.

This ability can only be used once per long rest.