So, a Ruby/Sapphire card that provides an ink ramp (a Sapphire hallmark) can be placed in a Ruby deck, providing more options and versatility
If the creature Audacity would enchant is an illegal target by the time the Aura spell resolves, the entire spell doesn't resolve
What Does Cumulative Upkeep Add Mana Do
Then, the more you play, you slowly start to discover other resources and concepts as well
Since all Modern cards should pass through Standard at a given point, WotC was having trouble feeding the format with new cards or reprints, since cards like Tarmogoyf and Cryptic Command would be too powerful for Standard (were talking about the 2013 MTG era, keep in mind)
Lets take a look at its use, history, and eventual fate