Level 4 ATK and DEF conventions

The "Rule of 2000" is a general rule that previously applied to Level 4 or lower Monster Cards, until the release of Gene-Warped Warwolf in Strike of Neos. The "Rule of 2000" stated that once Monster Cards got to 1900 ATK, to go further, to 2000 and beyond, Special Conditions had to apply to the monster to limit the card.

However, DEF does not have a "Rule of 2000", instead, it has a "Rule of 3000"; 2000 DEF Monster Cards are plentiful, and many Level 4 or lower Monster Cards are higher than 2000 DEF.

There is also a "Reverse Rule of 2000" that informally applies to high-level Effect Monsters. Typically Level 5 and higher monsters do not have ATK that is lower than 2000, unless the monster has a very powerful effect to balance it out (such as "Needle Burrower" or "Airknight Parshath"), or is intended to be a defensive monster with higher DEF than ATK. This was not the case in the early days of the game, when many high-level Normal monsters were being released that had what would now be considered very weak ATK and DEF for their Level.