Legality depends on the tournament format -- Urza, Lord High Artificer can be legal in some formats and banned or restricted in others
You can then pay the reconfigure cost to turn the creature into an equipment and attach it to a creature you control
Since youre on this list, you might well be wondering which of all these cards is the most expensive
Pokebeach mentions that these cards are worth around $36 and $39, depending on which Pokmon is portrayed and the market fluctuations
Sorin the Mirthless was only ever good when you were ahead and then not even that good against the crazy Leir, Disciple of the Drowned fueled endgame of the control decks
Myth Realized While it may seem like a big mana investment to put lore counters on Myth Realized, you can just use non-creature spells to fill it relatively quick, in decks with cheap instants or sorceries like Brainstorm or Preordain