Napoleonic Rage

You are imbued by the Rage often experienced by those of diminutive stature. When attacking an enemy, you can as a bonus action enter a mental Rage that lasts for one round unless extended by attacking the enemy again, or by using your bonus action to extend your Rage.

While Raging, you have resistance against Psychic damage, and advantage for saving throws against spells that deal Psychic damage.

You cannot maintain concentration while Raging, although you can still cast spells that do not require concentration.