The concept of the mana curve is important to all decks, but it's most clearly illustrated in the case of a fast creature deck
You can learn about how card condition affects value and a full breakdown of the most expensive cards by rarity tier, Those will help you make a better choice before any future trade or sale
Dont underestimate this card in Commander or any Limited format
Akal Pakal, First Among Equals, when you build around it, is a Chart a Course every turn for free
Gaston, Despicable Dealer is a potential replacement for Doc that can get you to your seven-cost characters sooner, but because it is not inkable it may be more difficult to fit it in
(Add it to your lore tracker.) A cards lore value can be found on the right-hand side of its text field, indicated by the number of diamond icons