The Big One

The Big One is probably the most cost effective grenade in the game (more powerful grenades, such as Thorium Grenade are extremely costly). It has enormous stun period, huge radius and good damage.

Source
The Big One is crafted by Engineers with a skill level of 235 who also have the Goblin Engineering specialty.

The recipe for this item is taught by Goblin Engineering trainers.

Goblin Engineering

 * Dimensional Ripper - Everlook