All cards must be singleton (one of each, no duplicates), and everything in the preconstructed deck must match the color identity of your commander
On the other hand, people who strongly support the substitute technique tend to focus on the instances in which this works well (dual lands) and gloss over the fact that some of the Reserved List cards most important to the Commander format (Wheel of Fortune and Gaea's Cradle) don't have substitutes that are anywhere close to their original
Getting 2/2s simply for playing Magic is a strong ability on its own, and opens up options for mana ramp, Voltron (making 1 creature super strong through powerups), Curses like Curse of Opulence for table politicking, and several other cool, unique effects that Auras can bring to the table as you build a token army
For example, if the enchanted player has 10 life and is dealt 1 damage, that damage will reduce their life total to 9
These are the error types that are genuinely collectible and can carry significant premiums over the normal version of the card