If the quest "army of the undead" does not complete, then perhaps some NPC is not killed. You need to check each enemy through the Union_MarvinHelper.vdf plugin. Some NPC may be "invisible" with the wrong position. Such NPC should simply be moved to the nearest point. (via ai_teleport). If the enemy is not in the world at all, then it should be inserted.

The algorithm is as follows:

1. Install marvin helper plugin
   https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2847617433
   and press ~ in game.
   
   
2. Check if NPC is dead or not (1 - killed, 0 - alive)
   call npc_isdead Knochenmagier_Athanos_07
   
   
3. If he is alive, then we will try to move to him.
   goto vob Knochenmagier_Athanos_07
   
   If there is no Knochenmagier_Athanos_07 in the hint in Marvin Helper, then this means that there is no such NPC in the world. Then you need to insert it yourself
   insert Knochenmagier_Athanos_07
   and kill
   
   If there is a hint, then we move to it.
   goto vob Knochenmagier_Athanos_07
   
   
4. Let's see, if we don't see the enemy, then we turn on the grid of waynet
   toogle waynet
   
   
5. Teleport "invisible" npc to the nearest point
   call ai_teleport Knochenmagier_Athanos_07 "WACHE_THRON_05"
   kill and turn off grid
   toogle waynet

Video: https://www.youtube.com/watch?v=YnxsjZZTp6g


List of NPC

Knochenfuerst_14005
SkeletonMage_Athanoskrypta
SkeletonMage_Athanosburg
SkeletonMage_Athanoswald
Knochenschuetze_Athanos_01
Knochenschuetze_Athanos_02
Knochenschuetze_Athanos_03
Knochenschuetze_Athanos_04
Knochenschuetze_Athanos_05
Knochenschuetze_Athanos_06
Knochenschuetze_Athanos_07
Knochenschuetze_Athanos_08
Knochenschuetze_Athanos_09
Knochenschuetze_Athanos_10
Knochenschuetze_Athanos_11
Knochenschuetze_Athanos_12
Knochenschuetze_Athanos_13
Knochenschuetze_Athanos_14
Knochenschuetze_Athanos_15
Knochenkrieger_Athanos_01
Knochenkrieger_Athanos_02
Knochenkrieger_Athanos_03
Knochenkrieger_Athanos_04
Knochenkrieger_Athanos_05
Knochenkrieger_Athanos_06
Knochenkrieger_Athanos_07
Knochenkrieger_Athanos_08
Knochenkrieger_Athanos_09
Knochenkrieger_Athanos_10
Knochenkrieger_Athanos_11
Knochenkrieger_Athanos_12
Knochenkrieger_Athanos_13
Knochenkrieger_Athanos_14
Knochenkrieger_Athanos_15
Knochenmagier_Athanos_01
Knochenmagier_Athanos_02
Knochenmagier_Athanos_03
Knochenmagier_Athanos_04
Knochenmagier_Athanos_05
Knochenmagier_Athanos_06
Knochenmagier_Athanos_07
Knochenmagier_Athanos_08
Knochenmagier_Athanos_09
Knochenmagier_Athanos_10
WaffenknechtZombie_Athanos_01
WaffenknechtZombie_Athanos_02
WaffenknechtZombie_Athanos_03
WaffenknechtZombie_Athanos_04
WaffenknechtZombie_Athanos_05
WaffenknechtZombie_Athanos_06
WaffenknechtZombie_Athanos_07
WaffenknechtZombie_Athanos_08
WaffenknechtZombie_Athanos_09
WaffenknechtZombie_Athanos_10
WaffenknechtZombie_Athanos_11
WaffenknechtZombie_Athanos_12
WaffenknechtZombie_Athanos_13
WaffenknechtZombie_Athanos_14
WaffenknechtZombie_Athanos_15
WaffenknechtZombie_Athanos_16
DemonLord_Athanosburg
Demon_Athanosburg_01
Demon_Athanosburg_02
Demon_Athanosburg_03
Demon_Athanosburg_04
Demon_Athanoswald_01
Demon_Athanoswald_02
Demon_Athanoswald_03
ErzGolem_Athanos_01
ErzGolem_Athanos_02
ErzGolem_Athanos_03
ErzGolem_Athanos_04
Gobbo_SkeletonAthanos_01
Gobbo_SkeletonAthanos_02
Gobbo_SkeletonAthanos_03
Gobbo_SkeletonAthanos_04
Gobbo_SkeletonAthanos_05
Gobbo_SkeletonAthanos_06
Gobbo_SkeletonAthanos_07
Gobbo_SkeletonAthanos_08
Gobbo_SkeletonAthanos_09
Gobbo_SkeletonAthanos_10
Skeleton_Paladin_Marbod
Skeleton_Paladin_Oliver
Skeleton_Paladin_Herbrandt
Skeleton_Ritter_Athanos_01
Skeleton_Ritter_Athanos_02
Skeleton_Ritter_Athanos_03
Skeleton_Ritter_Athanos_04
Skeleton_Ritter_Athanos_05
Skeleton_Ritter_Athanos_06
Skeleton_Ritter_Athanos_07
Skeleton_Ritter_Athanos_08
Skeleton_Ritter_Athanos_09
Skeleton_Ritter_Athanos_10
Skeleton_Ritter_Athanos_11
Skeleton_Ritter_Athanos_12
Skeleton_Ritter_Athanos_13
Skeleton_Ritter_Athanos_14
Skeleton_Ritter_Athanos_15
Skeleton_Ritter_Athanos_16
UndeadOrcWarriorAthanos_01
UndeadOrcWarriorAthanos_02
UndeadOrcWarriorAthanos_03
UndeadOrcWarriorAthanos_04
UndeadOrcWarriorAthanos_05
UndeadOrcWarriorAthanos_06
UndeadOrcWarriorAthanos_07
UndeadOrcWarriorAthanos_08
UndeadOrcWarriorAthanos_09
UndeadOrcWarriorAthanos_10
UndeadOrcWarriorAthanos_11
UndeadOrcWarriorAthanos_12
UndeadOrcWarriorAthanos_13
UndeadOrcWarriorAthanos_14
UndeadOrcWarriorAthanos_15
UndeadOrcWarriorAthanos_16
UndeadOrcWarriorAthanos_17
UndeadOrcWarriorAthanos_18
UndeadOrcWarriorAthanos_19
UndeadOrcWarriorAthanos_20
UndeadOrcWarriorAthanos_21
UndeadOrcWarriorAthanos_22
UndeadOrcWarriorAthanos_23
UndeadOrcWarriorAthanos_24
UndeadOrcWarriorAthanos_25
Harpie_Athanos_01
Harpie_Athanos_02
Harpie_Athanos_03
Harpie_Athanos_04
Harpie_Athanos_05
Harpie_Athanos_06
Harpie_Athanos_07
Harpie_Athanos_08
Harpie_Athanos_09
Harpie_Athanos_10
Harpie_Athanos_11
Harpie_Athanos_12
Harpie_Athanos_13
Harpie_Athanos_14
Harpie_Athanos_15
Harpie_Athanos_16
Harpie_Athanos_17
Harpie_Athanos_18
Harpie_Athanos_19
Harpie_Athanos_20
Undead_Troll_Black_Athanos