After my sojourn from Magic: The Gathering in 2003, after Mirrodin spoilers started to roll out, Ravnica: City of Guilds was the set/block that almost brought me back into the fold. I loved the idea of its multicolor theme (similar to the Invasion block) and storyline.
Basically, Ravnica is one giant cityscape where ten guilds, each a political faction and representative of a two mana color combinations among the five existing in Magic (Black/Blue/Green/Red/White), fight for control after a pact of peace — initiated long before — begins to crumble.
Even though the guilds are primarily based in the Ravnica plane of Magic's multiverse, they have been used to identify those color combinations ever since. They are as follows:
The Boros Legion (Red/White) | The Golgari Swarm (Green/Black) | The Selesnya Conclave (Green/White) | House Dimir (Blue/Black) | The Orzhov Syndicate (White/Black) | The Izzet League (Blue/Red) | The Gruul Clans (Red/Green) | The Azorius Senate (White/Blue) | The Cult of Rakdos (Black/Red) | The Simic Combine (Green/Blue)
Ravnica: City of Guilds focused on those first four listed — Boros, Golgari, Selesnya, and Dimir — the rest being introduced in the block's expansions, Guildpact and Dissention. Each guild/faction brought its own mechanic and/or ability.
Boros had Radiance, which was an ability that allowed its effects to spread to all other creatures sharing the targeted one's colors; Golgari had Dredge, which allowed players to place a card with the ability from the graveyard into their hand if they forfeit drawing a card and instead place the indicated amount of cards from the top of their library into their graveyard; Selesnya had Convoke, which allowed players to tap creatures to pay for some or all of a cards cost (each creature tapped reduced the cost of a card with Convoke by one mana of that creature's color, or by one colorless); and finally, Dimir had Transmute, which allowed a player to pay an amount of mana and discard a card with Transmute on it, letting the player then search their library for a card with the same converted mana cost (CMC) as the discarded card and put it into their hand.
This set also introduced Hybrid Mana (where cards could have a single mana cost paid by one of two types) and Shock Lands!
As much as I wanted to return during the original Ravnica block, I wouldn't until later down the road with New Phyrexia. However, there are still cards from the set that I really like, or that I know were popular, and I'll share some of them as I wrap up:
Do you currently play Magic: The Gathering? Are you a fan of Ravnica: City of Guilds? If so, what's your favorite card and/or ability/mechanic from the set? Which guild do you like the most from the set? From the block? What are your thoughts about Hybrid Mana? Was it a good addition to the game? Did you like that Ravnica was revisited down the road?