Might as well post this here, since it won't be horrifically long. The normal Prerelease Tactics article one might expect before Guildpact comes out is well...not coming out. For one thing, the online cardlist spoilers are not complete, and it would be terribly hard to make accurate comments about the value of any common when you haven't seen them all. Secondly, the legal hubub that occaisionally surrounds the release of new sets and related rumor information has risen up again at the last second, which is quite likely why spoilers remain incomplete.
That said, a little birdy told me a few things that can lead to some general observations. The first part is no big secret. The use of Prerelease cardsets tend toward encouraging the use of three colors. Given the guild structure of the Ravnica block and the available guilds at the Guildpact Prerelease, certain color triads are coming out stronger than others because you can get three sets of guild cards in. Orzhov/Selesnya/Golgari is one example with White/Black/Green, and Boros/Gruul/Selesnya is another with White/Green/Red. Play off your card supply as always, but one of those combinations will maximize the number of cards you can afford to use within your color base in your card pool, and that's a healthy thing. Also, the Izzet guild's focus on casting instants and sorceries is moderately unhealthy in a format that likes to be creature heavy. This, combined with the fact that blue is not included in any of the color triangles above, suggests we'll be seeing blue-light and green-heavy again. Ivy Dancers are tech.
As far as general comments about certain cycles, the Magemark auras all seem playable, but I wouldn't recommend making a habit out of using too Auras of any quality in Limited play...I made that mistake back in Scourge. The Orzhov Euthanist seems likely to take the prize of best-in-show common from the new set, and it would be wise to watch out for the Scab-Clan Mauler, a two-drop Gruul card that will surprise and overtake the unwary by setting off the entire Gruul strategy. The Silhana Ledgewalker will do much the same thing in an entirely different fashion. Don't let the Gruul get their engine rolling, because they're VERY difficult to stop once you do. Pillory of the Sleepless works well here.
Oh yeah. the Izzet guild-mana common, the Petrahydrox? Yeah, don't run him...don't feel sorry for the Izzet though. They'll come back in Constructed.
