(I'll give u a more clear description of Robert and the necklace cause I got like one comment abt it💪😍
When Robert was born, his heart had been replaced with the necklace from the cult cause they had seen the potential in him, it had the exact same functions as a normal heart.
And it had controlled him, only partly though, because hes more energetic and healthy since he's young, but as he gets older, the necklace will have more control over time. He doesn't support anything the necklace does, but he barely has any reaction to its actions since he's used to it by now.
much like how bob was controlled during his killing spree.
That's all I can really give you unless you want me to spoil the whole thing😰
Keep in mind, this is my personal interpretation of the cult and spooky month in general)