How to Defeat Legate in Fallout: New Vegas

Defeat Lanius using a Speech or Barter check. You will need either a Speech skill or a Barter skill of 100 to talk Lanius into retreating. In these scenarios, your character convinces Lanius that the West is too vast and too short on resources for the Legion to hold effectively. By following the dialog trees you will be faced with increasingly difficult Speech or Barter checks until you have convinced Lanius to retreat and avoided a battle altogether.

Use explosives. Lanius has more Hit Points (HP) and a higher Damage Threshold than a Deathclaw. Even if you have a high Small Arms skill and good weapons, bullets don't do much damage to Lanius.

Stay as far away from Lanius as possible. Lanius is a melee character, and even a high Endurance character takes a beating when Lanius gets too close. Unfortunately, Lanius is quick, and crippling his legs doesn't slow him down. If you can, avoid a melee battle with Legate.

Finish the battle as quickly as possible. Not only do Lanius's attacks deal tremendous power, but he periodically attempts to heal himself. As a result, slowly chipping away at his health is not an efficient strategy.

Use any weapons and drugs you have been saving. This is the last major battle in the game, so use any expensive or rare equipment you've been saving. Because the game is almost over, you won't have to worry about the long-term effects of becoming addicted to meds such as Jet or Buffout, and although Lanius is incredibly tough, a direct hit with a Fat Man could kill him.