Guild Mechanics for GRN:
Boros (R/W)-Mentor: When this creature attack, give another target attacking creature a +1/+1 counter if it has lesser Power than this creature.
Dimir (B/U)-Surveil: Look at the top X cards of your library, then put any of those cards into the graveyard or on top of your library in any order.
Golgari (B/G)-Undergrowth: Not a full mechanic, just a keyword that denotes that the following ability scales based on the # of creatures in your graveyard.
Izzet (U/R)-Jump-Start: You may cast Jump-Start cards from your graveyard, with the additional cost of discarding a card. Exile the Jump-Start card.
Selesnya (G/W)-Convoke: Returning mechanic, tap creatures to help cast spells.
Jump-start is mildly interesting depending on how safe they play it. They can afford to not-over-cost Jump-Start cards the way they have to overcost Flashback cards, since the "recast" still costs a card and the full mana cost. Surveil's going to feel very familiar with Explore still being around.
They talked about taking a different approach to convoke this time by having cards that reward you for tapping creatures for non-combat things.