From Halopedia, the Halo wiki
The Banished have appropriated Lich transports and repurposed them to function as carriers for the central command structures of their raider bases. They are capable of transporting full Banished outpost structures into the battlefield. They are also capable of carrying massive troop payloads and vehicles, and are capable of utilising their massive plasma cannon to deal heavy damage to enemy forces.
These Liches saw heavy use by the Banished during their campaign on the Ark against the forces of the UNSC Spirit of Fire in 2559. During the conflict, they were employed by Pavium and Voridus following the release of the parasitic Flood from the ruins of High Charity. Following the destruction of the Proto-Gravemind, a Lich was used by Atriox to transport personally to the site of the infection and begin cleanup operations.
Halo Wars 2
In Halo Wars 2, Liches are usually only found as a non-useable unit, responsible for deploying the Banished Banished outpost structure similar to the D81-LRT Condor for the UNSC. In Halo Wars 2: Awakening the Nightmare, the Lich Vanguard is a useable unit for players playing as Pavium. The Lich can be unlocked as the final leader ability available to Pavium. Once deployed, the Lich will circle an area for a while, using its heavy plasma cannon to fire upon assailants for massive effect similar to the Pelican Gunship ability available for Captain Cutter. Additionally, at the centre of the Lich's circling area will spawn a portal allowing the player to produce infantry and vehicle units. This makes the Lich vanguard an incredibly powerful area-denial tool.
List of appearances