Slash is an animation utility that brings onion skinning capabilities to Blender. It allows animators to view multiple frames simultaneously, making it easier to adjust poses based on previous or upcoming frames in a sequence. Users can display onion skins for all frames, a specific range, or manually selected frames. The tool supports displaying onion skins for multiple meshes at the same time and includes options for keeping original materials or applying custom colors and alpha values to the ghosted meshes. Additionally, it supports realtime playback preview and linked collections.