It shaped the way red turned out to be in the color pie, as Richard Garfield recalled in booklet found in From the Vaults: Dragons : The biggest effect of Shivan Dragon on how the Magic game turned out may be that its the biggest reason red has flying
The Immortal Sun - $25 As a six mana artifact that doesn't really do anything the turn it comes out, The Immortal Sun is a little overhyped, and we were quite surprised to see its $25 price tag
Chronicles made a far less cool version available and dramatically increased the supply, which took out most of his street cred, but he's back now as Nicol Bolas, Planeswalker behind the dreaded Conflux
You control the effect, so you use it on your turn, which lets you play cards like sorceries and creatures and even drop a land
Manglehorn is a wonderful Traverse the Ulvenwald bullet, and I cant imagine any green creature deck not having access to some number of Manglehorns in their 75