The depth of colors
The most basic idea of a master set is every card in the numbered set, every Secret Rare, and every reverse holo (which reprint the non-Full Art cards with foil on the card's border and text area rather than on the background of the art)

Advanced Search Sets Random Syntax Aang, Destined Savior Adeliz, the Cinder Wind Admiral Brass, Unsinkable Adult Gold Dragon Agatha of the Vile Cauldron Ahn-Crop Crasher Akki Drillmaster Akki Lavarunner Akoum Battlesinger Akoum Firebird Akoum Stonewaker Akroan Conscriptor Akroan Crusader Akroma, Angel of Wrath Akroma, Vision of Ixidor Akuta, Born of Ash Alaundo the Seer Alesha's Vanguard Alex Wilder, Runaway Alexios, Deimos of Kosmos Alibou, Ancient Witness Alibou, Ancient Witness Altac Bloodseeker Amber Gristle O'Maul Ambuscade Shaman Ambush Party Amethyst Dragon Amphin Mutineer Anathemancer Angel of Indemnity Anger Animus of Predation Anje Falkenrath Ankle Shanker Apprentice Necromancer Araumi of the Dead Tide Arbalest Engineers Arc Runner Arcbound Hybrid Arcbound Slasher Archfiend of Sorrows Archwing Dragon Arclight Phoenix Ardoz, Cobbler of War Ardyn, the Usurper Argivian Avenger Arni Brokenbrow Arthur, Marigold Knight Artificer's Dragon Asari Captain Ash Zealot Ash, Party Crasher Ashen Ghoul Ashen Monstrosity Ashling, the Limitless Ashnod's Harvester Assquatch Atalan Jackal Atraxi Warden Aurelia, the Law Above Aurelia, the Warleader Aurelia, the Warleader Avalanche Caller Avalanche Riders Avarax Avatar Kyoshi, Earthbender Awakened Skyclave Axebane Ferox Axgard Cavalry Ayara, Furnace Queen Badgermole Badgermole Cub

Having access to a Sun Titan at such a low mana cost is wonderful, and you should play it in your white decks
While you can buy just about any singles you need these days, its still hard to resist the excitement of opening a bunch of packs and seeing whats inside
As such, the design and artwork of cards found within Mirage are unlike anything in Magics history, before or since, so keep your eye on the horizon and youll spot something thats not a mirage: the most valuable cards from this over-20-year-old Magic set