Legendary means there can only be one copy on the field at a time
Richard Garfield, the games creator, has frequently issued special cards in small quantities to commemorate personal life events
Mageta the Lion (S, Block) While Blinding Angel might have heralded the return of white-blue control decks, Mageta the Lion pushed them over the top
Once per turn, Omnath, Locus of All can add mana to the mana pool if a revealed card has enough colored mana symbols, and in either case, the card will be drawn to restock the player's hand at no cost
For brewers, placing a price limit restricts access to a lot of the big players in the format, forcing you to get creative and search for alternatives (that will often end up better in the specific deck)