It pays homage to the original 2000 set that came out, well, 25 years ago now (feeling old yet?)
Modern cards carry significantly higher risk due to overproduction, reprint cycles, and speculative volatility
Ancestral Recall Balance Biorhythm Black Lotus Chaos Orb Channel Dockside Extortionist Emrakul, the Aeons Torn Erayo, Soratami Ascendant Falling Star Fastbond Flash Golos, Tireless Pilgrim Griselbrand Hullbreacher Iona, Shield of Emeria Karakas Jeweled Lotus Leovold, Emissary of Trest Library of Alexandria Limited Resources Lutri, the Spellchaser Mana Crypt Mox Emerald Mox Jet Mox Pearl Mox Ruby Mox Sapphire Nadu, Winged Wisdom Paradox Engine Primeval Titan Prophet of Kruphix Recurring Nightmare Rofellos, Llanowar Emissary Shahrazad Sundering Titan Sylvan Primordial Time Vault Time Walk Tinker Tolarian Academy Trade Secrets Upheaval Yawgmoth's Bargain Keep in mind that, in the early years of Commander, a second Banned as Commander list was maintained
I think its important to minimize the number of nongreen cards that cost more than one mana of the same color, but other than that, almost any card can work here
