While you can copy legendary Birds, you can only keep one of them, as the legend rule will still apply
Sets celebrating milestone anniversaries, featuring legendary Pokmon, or introducing new card types often generate significant collector interest
Literally everything from the design, cardstock, artwork is completely off
But sneak an attack in with these guys and watch out for cards that are way more busted than a 7/7 with trample, think along the lines of Bloodthirster, Worldspine Wurm, or Blightsteel Colossus
Other than triggering landfall, enabling delirium, delve, threshold, Tarmogoyf, Deathrite Shaman, Lotus Cobra (okay, enough), they thin out your deck and give you the dual/triland or the mana you need at the right time