Newer Super Mario Bros. Wii version 1.3.0 is the latest major update (released November 2021) for the popular fan-made overhaul of the original game. It is widely considered a "full unofficial sequel," featuring 128 new levels and a massive custom world map.
: Includes 128 entirely new levels spread across 14 unique worlds on a gigantic, fully connected world map. Creative World Themes
In Dolphin, go to Config > Paths and point it to your game folder.
The v1.3.0 update provided significant polish and bug fixes to the core experience, as detailed in the official Newer Team Changelog :