Most of us know how to build a powerful deck yet not many people can build an effective side deck. This is the biggest problem for most duellists as an effective side deck often separates the advanced players and the pro players who win big events. Here is an effective and practical way to build a useful side deck.

Start off with your finished deck, built to take on most decks. Now list the main decks you will have a problem duelling, and are likely to duel.

For each opposing deck change your deck with the minimum changes, usually 3 to 6 cards, to make your deck more powerful than theirs. Try to use the same cards for each opposing deck if possible. Write down the changes for each and reset to your original deck after each.

If any of your changes appear in each build, put it into your main deck.

Now check your notes and build your side deck using the most repeating cards and the most effective cards.

P.S. Try to keep in mind that you want to keep your side deck choices small, try to think of cards that work against multiple deck such as Skill Drain as opposed to Light-Imprisoning Mirror.