Grading MtG cards can be a costly exercise with minimal return, due to the fact that graded cards are returned in tamper-evident cases and thus need to be kept out of play in order to retain their grading, as well as the risk of rare cards being reprinted in newer sets and dramatically dropping the price
My top five powerful cards list, in no real order, is probably Sol Ring, Black Lotus, Recall, Time Walk and Academy
Monkey.D.Luffy ST08-001 (One Piece Starter Deck 8: Monkey.D.Luffy | One Piece Cards) prices are based on the historic sales
Most of the Legendary items with the ability to create token copies of themselves also do something to prevent them from falling victim to the Legend Rule
Menace and the Current MTG Meta Anti-blocking ability has always been an important mechanic in MTG
You could build around the legendary text or completely ignore it, though you'll probably want to lean on equipment for keywords like lifelink and deathtouch