To find the Alteci the player must have spoken to the "Huntmaster" in Phon Coast and defeated Thalassinon, which will trigger the start of the Rare Game quest.
The player must build a chain of twelve Mallicants (or Shambling Corpses from Athroza Quicksands) in The Undershore area of the Zertinan Caverns. Players do not need to leave and reenter to trigger the Alteci's appearance: one must simply scroll his spawnpoint off the minimap. The player should do this by going near an exit and then heading back towards the center of the room.
To make the spawning easier, the player can start the Mallicant chain in another area, as long as the twelfth perishes in The Undershore. The next area, Halls of Ardent Darkness, has many Mallicants—if the player kills eleven Mallicants here, moves into The Undershore and kills another, this will satisfy the requirements for the Alteci to spawn.