Is it just me or do the Nightmare Forces have a lot of similarities with the Dark Spirits?

Both have a possession-based catalyst (The Nightmare Entity and Vaatu), they are corrupted entities and their leader is somewhat parasitic and transforms their hosts into monsters (Luna and Rarity and Unalaq).

2779242 They are very similar indeed. They are both spirits from another world that are usually peaceful, but can be corrupted and turned dark. I noticed this immediately when Korra aired.