History of Thunderhead

Overview

Thunderhead is a Legendary armor set from Lightfall, themed around the Cloud Striders of Neomuna. Each piece carries a Cloud Strider quote as flavour text. It exists for all three classes: Hunter (Thunderhead Mask, Grips, Vest, Strides, Cloak), Titan (Helm, Gauntlets, Plate, Greaves, Mark) and Warlock (Cover, Gloves, Robes, Boots, Bond).

Acquisition

Destinypedia says each piece is unlocked by ranking up reputation with Nimbus on Neomuna, and the in-game source line is "Exploring Neomuna". Blueberries notes that Nimbus rank-ups reward engrams containing Neomuna gear but does not say outright that the set comes only from them, so check in game.

Set bonuses

Per We Want Destiny 3, you need four of the five pieces for the full bonus, leaving one slot for an Exotic.

• 2 pieces, License to Thrill: activating your grenade or the Nanotech Tracer Missiles origin trait grants stacking resistance to incoming damage at point-blank range.
• 4 pieces, Lethal Weave: defeating an unraveled combatant grants grenade energy; at max grenade energy you gain Special ammo meter progress instead. "Unraveled" refers to Strand unravel.

The bonuses belong to the newer armor set system, so the original Lightfall-era set had none; sources do not say exactly when they were added.