NPCs composing that spawngroup :

greater_plaguebone (25%)

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

citymist_56, range=53 (262,-334,-14)

greater_war_boned_skeleton (33%)
greater_war_boned_skeleton (34%)

citymist_59, range=33 (262,-354,39)

citymist_60, range=55 (225,-426,39)

a_fog_golem (33%)
a_lost_one (33%)

citymist_62, range=54 (227,-348,-14)

a_shadow (25%)
plaguebone_skeleton (25%)

citymist_88, range=66 (199,-396,275)

citymist_94, range=62 (249,-327,77)

citymist_116, range=83 (182,-378,65)

citymist_117, range=62 (214,-349,64)

citymist_125, range=19 (259,-369,255)

gyrating_goo (50%)
gyrating_goo (50%)

citymist_127, range=74 (219,-328,274)

citymist_128, range=98 (189,-325,274)