A stuck and defended Norn will end the game against Affinity, Merfolk, and Infect, not to mention causing serious problems for Twin and Abzan/Abzan Liege
Gandalfs Sanction In a spellslinger and/or storm deck, an opponent with a mana elf can just be domed for lethal out of the blue
Temporary hexproof, but a permanent buff for a single mana is pretty great, especially in 1v1 formats
#9 - Azami, Lady of Scrolls Arguably the very first good Wizard Commander, Azami, Lady of Scrolls started terrorizing tables immediately as soon as people saw how powerful it is to have a tap ability you can use without needing haste
Add utility lands
As the spoiler season continues, lets maybe take a look at a few other new (or new reprints) Legendary Creatures that Wizards adds to our wonderful format