Shaman is a green unused alien in the SDK. It is not fully animated and is not currently featured in the standard Jacob's Rest campaign. The Shaman uses a healing beam, like a Medic. It will follow other aliens around and switch targets based on whichever has taken the most damage. Since the Shaman shares the same color palette and design style of enemies included in the final version of the game, it is not considered to be one of the Beta Aliens.
Certain custom campaigns (such as Lana's Escape) make use of Shamans in a support role, as their AI and code is more-or-less complete.
When spawned in game via the asw_ent_create asw_shaman command, it will heal every alien except for other shamans. The shaman will not run unless it is trying to chase another alien to heal it.