Gatecrash Guild Mechanics Overview

Simic

Evolve is a deceptively potent mechanic.  If a creature enters the battlefield with a higher power or toughness than the creature with evolve, you put a +1/+1 counter on the creature with evolve, sort of the opposite of the Graft mechanic from Ravnica block.  These +1/+1 counters can result in huge card advantage, stealing creatures, or even ramping quickly into massive creatures or expensive spells.

Gruul

Bloodrush is a very powerful tool for aggressive decks.  By paying a mana cost and discarding the creature card from your hand, you can channel the power and abilities of a creature with this mechanic into a creature you already have on the battlefield that is attacking.  There is little subterfuge here... Just brutal and efficient force.  Great for aggro decks that need that extra little bit of reach.  It can put people into situations where they lose no matter how they block, but also runs the risk of creating opportunities for 2-for-1's.

Boros

Battalion triggers when you are attacking with three or more creatures, and this will happen a lot if you are playing Boros.  While some of the cards with this are a little underwhelming (i.e. limited fodder), some look to be powerhouses in upcoming weenie decks by making creatures indestructible, pumping creatures, or providing combat abilities.

Orzhov

Extort is a triggered ability that triggers off of you casting a spell.  When you trigger it, you are given the option of paying a black or white mana.  If you do, each opponent loses 1 life and you gain that much life.  It seems pretty crummy at first glance I'll admit... but couple it with a bunch of cheap spells and more than one permanent with this ability in play and it doesn't seem quite so innocent.  Or better yet, combine it with Cipher cards for a much larger boost.

Dimir

Cipher is the only mechanic that doesn't occur on permanents.  However, don't let that fool you; it still involves creatures.  Once a spell with cipher has resolved, you may exile it encoded onto a creature.  If you do, the creature 'gains' a triggered ability that allows you to cast a copy of the exiled spell whenever the creature deals combat damage without paying its mana cost.  That means you will be able to get two casts out of the spell the turn you cast it if you get through for damage, and the creature doesn't have summoning sickness.