From the Super Mario Wiki
Yggdrasil's Altar is a downloadable stage that appears in Super Smash Bros. Ultimate, and is based on the recurring location Yggdrasil from the Dragon Quest series. It was released alongside the Hero on July 30, 2019.
Characters are transported around different parts of the world of Erdrea via a single main platform. Slimes and Spirits of Lost Time have cameos on this stage, and Cetacea appears in the background. Occasionally, other platforms will fly onto the field. Treasure chests may also appear on said platforms; attacking them yields an item. However, some of these chests are actually Mimics in disguise. Upon being revealed, the Mimics will lunge in front of them, dealing damage if their attack hits. They can be defeated if they are attacked enough, leaving an item behind.
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