History of The Rock

The Rock is the catalyst perk of the Forerunner, an Exotic sidearm from the 30th Anniversary Pack that uses Special ammo. The perk is unlocked by the Forerunner Catalyst.

Effect

After a final blow with the Forerunner, use the alternate action within several seconds. The next thrown grenade becomes a fragmentation grenade for a short time. The perk consumes part of your ammo reserves. Destinypedia lists the cost as 6 ammo.

Catalyst

The catalyst is obtained from Banshee-44 after reaching rank 16 with Xûr and completing Magnus Opus II. Its upgrade requires 700 eliminations with the Forerunner.