If Mishra's Foundry becomes a creature and you haven't controlled it continuously since the beginning of your most recent turn, you won't be able to activate its first or last abilities, and it won't be able to attack (unless it somehow gains haste)
Even attaching Skullclamp to a larger creature is often worthwhile, as killing said creature will be risky for the opponents who don't want you to reap additional rewards.
Flores helped tune the list, and a short time later, it began a long and illustrious career of GP domination
The deck can is overall pretty strong, but does have consistency issues: goad can feel almost unfair against tables full of combat-focused decks, but doesn't offer much at tables with few creatures or heavy board wipes
(8/7/2020) The value of X changes as you gain and lose life
The most notable on the list is The One Ring from The Lord of the Rings: Tales of Middle-earth , the infamous card that only has one copy in existence