The undead have existed on Gaeleth for all of recorded history, but have played particularly strong roles since the War of the Undead in the early 1300s Avard. They are a class of organism unto themselves, powered by cohesive spells from the negative planes of energy. While some people believe negative planar energy to be a form of antimatter, this is not the case; negative planar energy is more akin to an entropic or lower order energy state that mimics conventional energy states.

Undead encounters can include:

Poltergeists (4E Dungeons and Dragons Open Grave)
Zombies (4E Dungeons and Dragons Open Grave, Monster Manual)
Wights (4E Dungeons and Dragons Monster Manual)
Ghasts
Skeletons (4E Dungeons and Dragons Monster Manual and Monster Manual II)
Wraiths (4E Dungeons and Dragons Monster Manual)
Hecuvae
Shadows
Ghouls (4E Dungeons and Dragons Monster Manual)
Mistrae