Vasavi Shakti

O Sun, Abide to Death.
Launcher Karna’s anti-army Noble Phantasm.
It is a spear made of lightning that will completely destroy anything in a single hit.
It can be thought of as the Hindu version of the Buster Launcher.
In the game he goes around busting stuff up with this. Karna has no idea himself, but between his appearance, and the wings that are scattered around when he uses this attack, he makes for quite the Visual Kei style Servant.

Fate/EXTRA Material: Encyclopedia of Fate/EXTRA

O Sun, Abide to Death. The Anti-Divine Noble Phantasm of Lancer of “Red,” Karna. A god-killing spear given to him by the thunder god Indra in the Mahabharata. The secret weapons among secret weapons, which doesn’t exist even in the treasure vault of the King of Heroes. Just as shown in the illustrations within Complete Material IV, his spear transforms and officially becomes this Noble Phantasm after he sheds his golden armor.
It’s not like the spear he usually uses is a fake, but it can’t activate its name of “Vasavi Shakti: O Sun, Abide to Death” in this state.

Fate/Apocrypha material: Fate/Apocrypha Encylopedia