Insistant Rage

When your health falls below a quarter of your maximum you can channel your rage and for 1d4 rounds your health is back to maximum and each hit you make against an enemy is a critical hit, following the duration you immediately fall to 0 hit points. Your AC is halved, and each hit scored against you is also critical. If you fall to 0 before the duration ends you immediately fail two death saving throws.

You can use this ability once per long rest