For an example of what Topps 1951 cards looked like, take a look below: For that series only, it was framed to be more like a game (a trading card game, perhaps?) , and each players cards could affect the game, such as drawing a strike or a ball card would mean your pitcher threw a strike or a ball, etc
Admittedly it is very effective at that, but you have to consider that a giant creature like that is of absolutely no use in the early game, before you've accumulated the 10 mana required to cast it, which is when you typically need the secondary effects of your finishers most
Retreat Cost: 1
When it comes to pure value, however, I must say Mox Jasper tops my list
Forbidden Droplet is ranked among the strongest cards in Yu-Gi-Oh
This allows you to use potentially powerful cards like Constant Mists and at least get a powerful creature to replace the land you lose