This format follows all of the normal rules of deck construction - meaning you build a 60-card minimum main deck with a sideboard of up to 15 cards, with no more than 4 copies of any one card across your entire deck list (excluding any basics)
Cards can be changed if theyre too powerful (either by having a higher mana cost or by having abilities removed) or if theyre not powerful enough (either by having a lower mana cost or by having abilities added)
Before I get into it, let me show a quick table comparing lands people run in tournament decks and what the equivalent would be in Commander decks: For tournament decks, 22 lands is the bare minimum unless your deck is very aggressive and made up nearly exclusively of one-drops
The top three begins with one of Eevees original evolutions: the fire type, Flareon
Instead, players would choose one of the two types of Pokmon cartridge (Red and Blue versions were available, each with slight variations in which Pokmon were available to catch) and, in order to complete their collection, would need to trade with other players using the Game Boy Link Cable