More Confirmed Information
8. Your guild signet serves many functions: First, it provides you with identification for other members of your guild, and for members of (loosely) allied guilds.
Second, it provides your 'core' two mana points, dictating what type of spells you can cast. If a player switches guilds, he receives a new signet and these core mana points are altered to reflect his new guild. If a player chooses to remain unaligned, he loses that second mana point that would have come with the sigil, but is not limited to two colors and may cast more versatile spells.
Third, your signet acts as an emergency reserve for magical energy. By returning to one of your guild's headquarters or safe houses, your signet will recharge, providing you with enough mana to cast a few spells should you find yourself in an area where you cannot access mana of your colors. When a signet is empty, it is useless until given ample time to recharge (more info on this later).
9. We will not be using spells as large in scope as those in the card game, most likely. In the game, it is assumed that, for the most part, Planeswalkers are tapping into vast reserves of mana to cast massive spells, whereas the PC's are not Planeswalkers, so their spell casting will be on a smaller scale.
10. There are nine playable races: Humans, Ogres, Elves, Dryads, Goblins, Viashino, Centaur, Loxodon, and Vedalken. More races, such as Minotaur and Cyclops, may come later. These races have predispositions for guilds, but are not required to join a certain guild in order to be played (Vedalken may join Orzhov, Centaur may join Rakdos, etc...)