Complex sentence: Sif and Balder use a Norn Stone to turn invisible and evade the Destroyer and discover Garm, who tells them that Hela freed the Destroyer from its crystal prison but a spirit possessed the armor before she could do anything and imprisoned Hela and Garm.
Split into simpler sentences: Sif and Balder use a Norn Stone to become invisible and evade the Destroyer. They meet Garm, who tells them that Hela freed the Destroyer from its crystal prison but a spirit possessed the armor and imprisoned Hela and Garm.