NPCs composing that spawngroup :

an_alarm (72%)

an_immobilizer (72%)

an_inactive_trap (72%)

a_blast_of_heat (72%)

a_dark_entity (72%)

a_low_hum (72%)

a_magi_construct (72%)

a_null_field (72%)

a_wardstone (72%)

a_wizard_construct (72%)

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

necropolis_42, range=67 (1695,3,-155)

an_amorphous_mass (60%)
an_amorphous_mass (60%)

necropolis_92, range=43 (1708,96,-152)