As the saying goes, if there are still two left they are valuable, if there's only one it is priceless
Lands that become basic are no longer nonbasic lands
Crystal, Inhuman Princess The color identity for Crystal, Inhuman Princess unfortunately means its playability is restricted, though it's quite good in the decks that support it
Part of this is due to flashback letting you use it twice, and part of it is the political angle for Commander: You can put counters on other players permanents to strike deals or maybe enhance cards like Generous Patron and Nils, Discipline Enforcer
In theory, you can balance out the mana loss by playing two lands on the following turn, but if Zell gets removed youll be left down a land and in a very nasty spot
That high value might not stick around forever though - a copy can still be worth thousands of dollars, but other promos have overtaken the tailor over time