Avenge (Common1) (R/W)
Instant
Avenge deals 4 damage to target creature that dealt damage this turn.
Azorius Ancestor (Common2) 1W
Creature – Spirit
1/2
Flying
When Azorius Ancestor enters the battlefield, exile target nonland card from a graveyard. Decree – Spells with the exiled card's name cost your opponents 2 more to cast.
Gilded Griffin (Common3) 2W
Creature – Griffin
3/1
Flying
Whenever you cast a multicolored spell, Gilded Griffin gets +0/+2 until end of turn.
Civil Authority (Common4) 5W
Enchantment – Aura
Enchant creature
Enchanted creature gets +3/+3, has vigilance, and can block an additional creature each combat.
Feral Watchwolf (Common8) 3(G/W)
Creature – Wolf
3/3
Isperia’s Gaze (Common9) (W/U)
Sorcery
Tap target creature. That creature doesn’t untap during its controller’s next untap step.
Ivory Elephant (Common10) 4W
Creature – Elephant
3/5
When Ivory Elephant enters the battlefield, return another permanent you control to its owner's hand.
Judge's Apprentice (Common11) 2(W/U)
Creature - Vedalken Advisor
1/4
When Judge's Apprentice enters the battlefield, reveal the top card of target player's library. Decree – Spells with the revealed card's name cost your opponents 2 more to cast.
Master of Ceremonies (Common12) 2W
Creature – Centaur Cleric
2/3 Congregate – When Master of Ceremonies enters the battlefield, you gain 1 life for each creature you control.
Noble Stoic (Common13) 1W
Creature – Human
1/1
When Noble Stoic enters the battlefield, choose a guild –
Selesnya – Destroy target enchantment.
Azorius – Target player can't cast spells this turn.
Phantom Armor (Common14) W
Enchantment – Aura
Enchant creature
Enchanted creature gets +1/+2.
If enchanted creature would be destroyed, instead remove all damage from it and destroy Phantom Armor.
Restraining Order (Common15) 3W
Enchantment – Aura
Enchant creature
Enchanted creature can't attack or block, and its activated abilities can't be activated. Decree – Spells with enchanted creature's name cost your opponents 2 more to cast.
Shield Tactics (Common16) W
Instant Congregate - Until end of turn, target creature gets +0/+1 for each creature you control. Untap it.
I think your hybrid creatures are pushing the envelope a little more than I'd be comfortable with (3/3 vigilance cards have almost always been uncommon or costed at 5 mana, for example, and although 2/1 strikers for 2 are now a thing, I don't think they're a hybrid thing yet). The only one I wouldn't increase the cost of by is Boros Barricade, and that's mostly because I really, really dislike it anyway because I see no justification that a card you can cast for should have flash. I note a certain love for really cheap hybrid spells? Not a complain as such, but it may affect how the set plays in unexpected ways.
Other than that, these are fairly serviceable commons besides Restraining Order, which may well be an uncommon. I'm surprised to see only one congregate card, though. It seems to me like Decree is more the type you want to play down a little at common/overall, while congregate fits the usual amount of guilds common more easily.
(R/W)
Instant
Avenge deals 4 damage to target creature that dealt damage this turn.
Azorius Ancestor (Common2)
1W
Creature – Spirit
1/2
Flying
When Azorius Ancestor enters the battlefield, exile target nonland card from a graveyard.
Decree – Spells with the exiled card's name cost your opponents 2 more to cast.
Gilded Griffin (Common3)
2W
Creature – Griffin
3/1
Flying
Whenever you cast a multicolored spell, Gilded Griffin gets +0/+2 until end of turn.
Civil Authority (Common4)
5W
Enchantment – Aura
Enchant creature
Enchanted creature gets +3/+3, has vigilance, and can block an additional creature each combat.
Conclave Sentry (Common5)
(G/W)
Creature – Elf Soldier
1/1
Vigilance
Epitaph (Common6)
(W/B)
Instant
Exile target card from a graveyard. Draw a card.
Beheading (Common7)
1(W/B)
Sorcery
Destroy target tapped creature.
Feral Watchwolf (Common8)
3(G/W)
Creature – Wolf
3/3
Isperia’s Gaze (Common9)
(W/U)
Sorcery
Tap target creature. That creature doesn’t untap during its controller’s next untap step.
Ivory Elephant (Common10)
4W
Creature – Elephant
3/5
When Ivory Elephant enters the battlefield, return another permanent you control to its owner's hand.
Judge's Apprentice (Common11)
2(W/U)
Creature - Vedalken Advisor
1/4
When Judge's Apprentice enters the battlefield, reveal the top card of target player's library.
Decree – Spells with the revealed card's name cost your opponents 2 more to cast.
Master of Ceremonies (Common12)
2W
Creature – Centaur Cleric
2/3
Congregate – When Master of Ceremonies enters the battlefield, you gain 1 life for each creature you control.
Noble Stoic (Common13)
1W
Creature – Human
1/1
When Noble Stoic enters the battlefield, choose a guild –
Selesnya – Destroy target enchantment.
Azorius – Target player can't cast spells this turn.
Phantom Armor (Common14)
W
Enchantment – Aura
Enchant creature
Enchanted creature gets +1/+2.
If enchanted creature would be destroyed, instead remove all damage from it and destroy Phantom Armor.
Restraining Order (Common15)
3W
Enchantment – Aura
Enchant creature
Enchanted creature can't attack or block, and its activated abilities can't be activated.
Decree – Spells with enchanted creature's name cost your opponents 2 more to cast.
Shield Tactics (Common16)
W
Instant
Congregate - Until end of turn, target creature gets +0/+1 for each creature you control. Untap it.
Sky Warden (Common17)
2WW
Creature – Human Knight
2/4
Flying
Vigilance
Wojek Cadet (Common18)
2(R/W)
Creature – Human Knight
2/1
First strike
Other than that, these are fairly serviceable commons besides Restraining Order, which may well be an uncommon. I'm surprised to see only one congregate card, though. It seems to me like Decree is more the type you want to play down a little at common/overall, while congregate fits the usual amount of guilds common more easily.
EDIT: Except reducing Decree. Each guild mechanic has five commons, three uncommons, and two rare/mythic.