Risk of Rain 2: Unused Mithrix Spawn State
I replicated this by replacing his EntityStateMachine's Initial State from whatever it is originally to "Assets/RoR2/Junk/Characters/Brother/EntityStates.BrotherMonster.ThroneSpawnState.asset" or if you're using runtime inspector, "EntityStates.BrotherMonster.ThroneSpawnState".
In the "moon" scene there's a throne there on the first phase.