Adventure Time (2010)

S8E4 Lady Rainicorn of the Crystal Dimension

Jake's son stumbles upon a mysterious box, which unexpectedly captures the interest of a Rainicorn. This enchanting creature becomes intrigued by the box's contents, leading to an adventurous encounter that unfolds in the magical Crystal Dimension. As they explore, Jake's son discovers the unique powers of the Rainicorn and learns valuable lessons about friendship and imagination.