NPCs composing that spawngroup :

plaguebone_skeleton (33%)

spectral_courier (33%)

spectral_courier (34%)

NPCs spawning around that spawngroup :
(Max range : 100)

citymist_105, range=39 (-241,-474,75)

citymist_135, range=85 (-242,-354,5)

citymist_136, range=51 (-245,-391,4)

citymist_141, range=87 (-139,-422,5)

plaguebone_skeleton (25%)

citymist_147, range=97 (-162,-513,5)

citymist_148, range=75 (-235,-513,5)

a_shadow (25%)
greater_spurbone (25%)

citymist_151, range=58 (-231,-496,3)

citymist_156, range=56 (-188,-395,4)

a_shadow (25%)
greater_spurbone (25%)

citymista_War_Bone_Overlord00035094065, range=64 (-215,-374,20)

a_War_Bone_Overlord (10%)
greater_spurbone (90%)

citymist_spectral_courier0_takp_import_v0, range=97 (-161,-512,5)

citymist_223157_takp_import_v0, range=88 (-260,-519,75)

gyrating_goo (100%)

citymist_222977_takp_import_v0, range=42 (-245,-475,75)

citymist_223158_takp_import_v0, range=91 (-261,-522,75)

gyrating_goo (50%)
gyrating_goo (50%)

citymist_222966_takp_import_v0, range=86 (-241,-353,5)

citymist_greater_spurbone86_takp_import_v0, range=94 (-219,-532,3)

greater_spurbone (50%)
greater_spurbone (50%)

citymist_222960_takp_import_v0, range=74 (-234,-512,5)

citymist_222958_takp_import_v0, range=64 (-224,-374,5)

citymist_222956_takp_import_v0, range=81 (-144,-433,5)

citymist_222955_takp_import_v0, range=88 (-138,-421,5)