From Shadow Era Wiki

Undead is a tribe of allies in Shadow Era.

They were introduced in Call of the Crystals with further support in Dark Prophecies and Shattered Fates. Currently all Undead allies are Shadow allies (with the exception of Popsickle, which is a Mage Ally). Visually, Undead allies resemble various dark and skeletal beings. Many have effects dealing with the graveyard. Many of them have Ice type attacks.