Energy unit. Can transform and condense mana.
Humanoid turrets, these robots have very little mobility but can blast apart any enemy that comes within range with a selection of high-power spells.
Their numbers are a bit strange for casters though. Their base Stats check out; low Health and Strength, high Mana and Magic. However their Health Growth is very high, matching their Magic Growth, while their Mana Growth is almost non-existent. You probably want to go with percentage increasing Traits over Stat Growth boosting ones for their Mana.
Their survivability isn't an issue either, between their Health Growth, natural Armor, and the rare Crystal type that halves most damage types and makes them immune to Bleeding, Burns and Poison. Making them Magic Level Types for more damage won't put them at risk.
Default E Units have no special use on the Overworld.
They can condense 10 crystal fragments and 100 crystals into a condensed crystal on their character screen at Home. Extremely useful as condensed crystals are in limited supply and are required to craft some powerful equipment, particularly if you're aiming for the true end.