wen when King Sombra was blasted with the power of the crystal heart he wasn't killed he was purified and sent to the realm of Shadows where he meets a Alicorn Colt named Hope. banished to the realm of Shadows due to his unstable Magic and was left alone for over 90000 years because of this he has a great distrust of mares.
wen Sombra showed up in the realm of Shadows Hope obviously becomes attached to him going as fare as say that Sombra his. Hope bin alone for so long the idea of being alone truly terrified Hope. Hope himself is timid by nature but While he is kind and friendly with Sombra, Hope is initially bitter, vindictive, and mistrusting towards all mares believing they are the true evil of this world, due to idly leaving him trapped in the realm of Shadows.

Ninety thousand years? yikes, any sentient being would gone insane by then

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he's emotionally scarred but he still quite sane, but he is prone to have deadly panic attacks that could potentially destroy wide areas.