This Legendary Gem reduces all non-Physical damage taken by 10%. You can only level this Gem to rank 100. Every upgrade will increase the damage reduction by another 0.5% up to a maximum of 60% total. The rank 25 bonus is one of the strongest in the game. It increases your resistance to Cold, Fire, Lightning, Poison and Arcane by 75% while below 50% Life. This secondary alone is about an additional 40% total damage reduction to non-Physical damage. Alltogether these 2 effects combine for approximately 75% total non-Physical damage reduction.
Esoteric Alteration Best Use
The #1 toughness Gem: Used by Supports and Damager Dealers alike. Can be super useful especially at lower Paragon levels early on in the Season, but is mostly outclassed in the endgame by offensive Gems or other supportive choices.
Legendary Gem in Diablo 3
Legendary Gem Creation:
If you need extra Legendary Gems to level up, you can make the Rift Guardian in any Greater Rift drop a new Rank 0 Gem by removing all the Legendary Gems with the same name from your Equipment, Inventory and Stash.
The safest way to do that is to put them into the Inventory of different character.