Fungus Beer

Night Goblins are especially cowardly creatures, but unlike those of other Goblin tribes, they have been known to create and consume an intoxicating brew called Fungus Beer, which enables them to fight in a near maniacal state, where they are completely insane and paranoid, and would enhance a Night Goblins senses and reflexes, enabling them to fight far better against other stronger foe.

Source

 * : Warhammer Armies: Orc and Goblins (8th Edition)
 * : pg. 52