Ironman
An ironman is similar to a crew battle, but it is between two people instead of two groups. It is an idea of g-regulate on SmashBoards based on Overswarm's idea.
Procedure
Both players pick 5 different characters. Each character starts with 4 stocks, for a total of 20 stocks. They then pick their opening characters before the battle. They start on a random neutral stage, but they can agree on the opening stage.
When a player loses all of their character's stock, they pick another character and counter-pick a legal stage. Each player starts the battle with their remaining stock, and therefore self destructs to match their previous stocks from the last game. If a player loses their 15 stocks, they lose the match.
Full roster ironman
This type of ironman is similar to a normal ironman, but involves the full roster. It is usually done as a side-event at many tourneys, one of the most famous instances being Mango and Mew2King's full roster ironman at Smash the Record.