Although we haven’t been able to test these effects just yet, it would appear to work in a similar manner to the Gleaming Incarnate Thunderstone in Season 1 and Obsidian Aspectral Earthstone in Season 2, both of which unlock additional graphics for their respective seasonal tier sets.
The additional graphical effects on Warrior Season 1 and 2 tier sets.
Players who complete Neltharion’s Legacy will instead unlock special effects for the Cavern Delver’s Gear, of which there are actually six variations awarded from various activities in recent patches – the Patch 10.1 campaign, Rare Mobs, World Quests, PvP, Time Rifts, and the Dawn of the Infinites mega-dungeon.
The Plate variant of Cavern Delver’s Gear, minus the extra effects from Ambrosial Sporestone.