Certain exceptionally powerful Pokemon called V, VSTAR, and VMAX are worth two, two, and three respectively
Dig Through Time is excellent for combo decks especially, because seven cards is a lot to look at
I now have about 90% of a 1st Ed Base binder set completed
Yami Yugi Seto Kaiba Joey Wheeler Mai Valentine Ta Gardner Yugi Muto Weevil Underwood Rex Raptor Mako Tsunami Yami Marik Marik Ishtar Yami Bakura Bandit Keith Ishizu Ishtar Odion Maximillion Pegasus Mokuba Kaiba Paradox Brothers Arkana Bonz Espa Roba Tristan Taylor Lumis and Umbra Duke Devlin Solomon Muto Rebecca Hawkins Serenity Wheeler Noah Kaiba Yami Yugi When Yugi Muto solved the Millennium Puzzle, he was infused with the ancient spirit of Yami Yugi
Playability If a card fits multiple decks or formats it gains demand from players, not just collectors
This obviously causes a great deal of issues for your table and can also be built around by including incredibly expensive spells to hit