20XX has become the go to hack pack for Super Smash Bros. Melee training, and its most recent update has made it even more effective in leveling up.
Added recently is its ability to record and replay save states, allowing you to practice for various situations in Melee. This is not unlike Street Fighter V‘s recording function, but has a few more extensible options, including infinite loops and state resets, which allow you to reset your exact position to set up various circumstances that you should practice for. It is, however, a little cumbersome to use, which is why SSBM Tutorials created a video chronicling how to use it properly.
Source: SSBM Tutorials