Recently I've been workshopping ideas for a set built around four-color guilds: Creatures, keywords, flavor identities, and all the rest. So far I've been working with the precedents set by the four color commanders in Commander 2016, and the fantastic advice of Game Knights' Jimmy Wong: "Powerful four color cards should be built around the color they aren't, not the colors they are".
With this, I've devised five keywords and playstyles to suit each of the four-color sets. They are as follows:
Sharpened — (An effect that in some way rewards having toughness 3 or less.)
Whatever this guild's culture is, I picture it being made out of many X/2 artifact creatures, or zombies, or drakes, or goblins, or other miniature things with toughness 3 or less, whose power is boosted by any number of equipments and auras. Furthermore, this directly contradicts the incredibly green mechanic of rewarding "power 4 or greater."
Stockpile N (You may have this creature enter the battlefield tapped. If you do, put N +1/+1 counters on it.)
This is a simple mechanic that I am simply proud of! This is a direct inversion of the red aspects of Riot, mixed in with blue ETB Choices and Outlast. It rewards the exact opposite of red creature play: slow and steady.
Grace — If no creatures have died this turn, (Reward).
The direct opposite of the VERY black mechanic that is Morbid! Given the number of ways that WURG can remove creatures from its benevolent calculations without killing them (exile, return to hand, evasion, etc.), I believe it's only fair to reward players for not killing opponents' creatures!
Provoke (Whenever this creature attacks, you may have target creature defending player controls untap and block it if able.)
Provoke is an old mechanic from Tempest, and I am absolutely using it for this color combination. Blue loves to evade. Provoke directly punishes evading the untapped creature, as otherwise there is no reason to untap it. In addition, Black is the only color in this guild that Provoke wasn't found in, and even then, that's nothing a little deathtouch can't fix.
Solitary N (This creature gets +N/+N if it is the only creature you control.)
Simple mechanic, simple explanation: White's main creature-based playstyle is to go wide rather than tall, with many individual token creatures rather than one big goody. Solitary gives you that one big goody. Unfortunately (or fortunately, depending on how you look at it) this guild should and would have many sacrifice outlets.
And with that, that's all my mechanics!!! If you all have any suggestions for the flavor of these groups, or the mechanics therein, please feel free to comment! I'll be eagerly waiting til then.