NPCs composing that spawngroup :

a_slag_sentinel (50%)

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

thundercrest_monocle_232, range=91 (-441,2252,127)

an_Isle_apothecary (50%)

thundercrest_monocle_234, range=83 (-510,2252,127)

an_Isle_talonstriker (50%)
Kodama_the_Voltaic (50%)

thundercrest_monocle_270, range=23 (-498,2311,177)

an_Isle_clawguard (50%)

thundercrest_monocle_278, range=47 (-439,2332,183)

a_bulwark_sentinel (50%)

thundercrest_monocle_282, range=42 (-476,2291,177)

an_Isle_talonstriker (50%)

thundercrest_monocle_8_2, range=47 (-439,2332,183)

a_rock_sentinel (50%)

thundercrest_monocle_8_61, range=42 (-476,2291,178)

an_Isle_guardian (50%)

thundercrest_monocle_8_62, range=91 (-441,2252,129)

an_Isle_guardian (50%)

thundercrest_monocle_11_3, range=47 (-439,2332,183)

a_stone_sentinel (50%)

thundercrest_monocle_11_28, range=91 (-441,2252,129)

an_Isle_guardian (50%)

thundercrest_monocle_11_29, range=83 (-510,2252,129)

an_Isle_reawakener (50%)

thundercrest_monocle_11_33, range=42 (-476,2291,178)

an_Isle_windraker (50%)

thundercrest_monocle_12_35, range=47 (-439,2332,183)

a_stone_sentinel (50%)

thundercrest_monocle_12_100, range=57 (-461,2383,178)

an_Isle_defender (50%)

thundercrest_monocle_12_103, range=89 (-573,2311,168)

an_Isle_defender (50%)