To defeat the narcissist, your attack must be two pronged. You must fight them from two fronts, so as to cause them to retreat into danger.
First, you must weaponise cheerfulness. When around them you must be cheerful as possible, and laugh off, defeat with logic, or ridicule their aggression. Constantly include them in conversations, sing (about them if necessary) enjoy the weather, birds, animals, anything at all. Ceaselessly praise their rivals, laugh at, own and accentuate their put-downs. Gentle teasing will enrage them no end. When they snap, be sure to tell them to take it easy.
Secondly, you must encircle them, cultivating good relationships with everyone around them. Speak ill of the narcissist in subtle ways, hoist the red flags without being too overt, let them know about anger management issues. You can even do this by having discussions about people with detestable qualities just like the narcissist – laziness, selfishness, baby rage.
As their rage increases, they will seek the assistance of all those people against you, but discovering they are favorable to you, the people you have warned will turn on them instead, thus sealing their fate.
The end is important in all things,
Robert