The most important of these is their -X ability
Lets say, for example, that youre playing a Red and Black deck, and you find yourself in desperate need of a board wipe

First up, here's a rank of the legendary creatures whose reprints are a price increase, sorted roughly by current price of the original printing: Thrasios, Triton HeroThrasios, Triton Hero Urza, Lord High ArtificerUrza, Lord High Artificer Yawgmoth, Thran PhysicianYawgmoth, Thran Physician Najeela, the Blade-BlossomNajeela, the Blade-Blossom Atraxa, Grand UnifierAtraxa, Grand Unifier Isshin, Two Heavens as OneIsshin, Two Heavens as One Vial Smasher the FierceVial Smasher the Fierce Yuriko, the Tiger's ShadowYuriko, the Tiger's Shadow Kenrith, the Returned KingKenrith, the Returned King Teferi, Mage of ZhalfirTeferi, Mage of Zhalfir K'rrik, Son of YawgmothK'rrik, Son of Yawgmoth Syr Konrad, the GrimSyr Konrad, the Grim Traxos, Scourge of KroogTraxos, Scourge of Kroog Captain Lannery StormCaptain Lannery Storm Danitha Capashen, ParagonDanitha Capashen, Paragon Fynn, the FangbearerFynn, the Fangbearer And the following is the remaining 20 legendary creatures, again sorted roughly by the price of the original printing

In 2003, following a first-time playthrough of the legendary Kingdom Hearts game, I scrounged every penny I could and saved for a copy of Final Fantasy VII for the original Playstation
It protects you completely