"Elder" is an effect found on the Elder Armor and Shoggoth sets.
In previous versions, there were 2 kinds of Elder Armor buff. One Is warangels Clenched fist and the other is Gargoyle Statue buff. The Warangel version grants radiation, heat, sulfur, cold, liquid nitrogen, and (vanilla) poison immunity while also granting breath protection. The Gargoyle (or "true" Elder buff) also grants Bio-Ooze, Shadow Gas, Proto poision immunity while also granting immunity against slush and snow slowdown.
As of the latest version however, the War Angel buff has been renamed "Superior" and its icon changed to avoid confusion.