Artillery Sphere is a 
Ripper Grenade
Its special effect is Orbiting Body - On equip, spawns an orbiting Observer that deals damage to nearby enemies. The Observer will briefly attack enemies damaged by the grenade.
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How to Unlock The Legendary Artillery Sphere Grenade
Legendary Loot
Weapons
Overview
How to Unlock
Unlock Location:
- Progress through the (A Zane to Kill For) DLC until reaching the Final Boss Biff Fistful
Farm Method:
- Defeat Biff Fistful to get a chance at the Artillery Sphere.
- After use the Encore Machine nearby to reset the fight.
- Repeatedly defeat Biff Fistful until the Artillery Sphere drops.