The Lich were used as an elite Thrall unit. Soulblighter used these to attack Baeldun and the Seventh Legion repeatedly. The Lich were created by Soulblighter and were very deadly. They could move faster than thrall and attack with powerful mace strikes. They were dark covered figures that wore black hoods and black armor.
It should be noted that in Myth 3 the Wolf Age, a Lich was a female banshee like undead that could fire green beams at you that caused many green hands to come up from the earth and drain the targets of their life energies. Basically in Myth 3 they functioned like Myth 1 & 2 Fetch.