The most valuable creatures in draft are those with evasion (Wind Drake, Gluttonous Zombie), a high power/toughness to mana cost ratio (Trained Armodon), or both (Shivan Dragon)
A card that doesnt have a mana cost is considered to have a mana value of 0
Some are obtained through Wonder Picks, where there's 1 in 5 chance of players pulling the desired card, and chances go up if there is more than one copy of that promo card in the pick pool
If you discarded a nonland card, put a +1/+1 counter on this creature.) Except for the listed exception, Copycrook copies exactly what was printed on the original creature and nothing more (unless that creature is itself copying something or is a token
The ability to trade would require there to be no limit on how many cards you can own
There are a lot of different box toppers, which means the range on how valuable these cards are varies heavily