The Selesnya Conclave

The Selesnya Conclave is a green/white guild from the plane and city of Ravnica. It strives for harmony between civilization and nature.

Founded by parun Mat'Selesnya, a female humanoid elemental formed via the fusion of dryads, the Selesnya Conclave is a decentralized collective variably described as a "selfless, nurturing, spiritual group" or a "brainwashing nature cult."
It involves itself in the establishment and maintenance of peace, life, and unity in Ravnica. The Conclave was appointed, along with the Azorius Senate, Boros Legion, and Orzhov Syndicate as one of the four guilds responsible for Ravnica's legal system: "The Selesnyan Conclave shall be the living spirit of the law," charging the Conclave with interpreting the intent of the lawmakers, although the Senate's interpretation of the law ultimately trumps that of the Conclave (Guildpact Statutes, Article I, Section 2). Because of this appointment as a historian of the law's intent, the Conclave has always found it necessary to preserve the city's history.

The territories held by the Selesnya are open and sunny, full of green spaces and gardens, with white stone buildings which are often open to the air.
Despite their appearance of being "good" and "peace-loving", in truth the guild has a sinister streak.
The Conclave used to employ its quietmen and other members to silence the civilians of Ravnica. The defenders of the Selesnya are the Ledev Guardians. Equenauts ride pegasuses, combining the role of mounted warriors and scouts. Sagittars are an order of elven archers that defend key guild locations.

Selesnya decks lay the groundwork through board-affecting enchantments or auras to pump their creatures or hinder their opponents.

• Main races: Pegasus’, Centaurs, Dryads, Loxodon, Humans, Wolves, Elves, Elementals
• Main classes: Knights, Archers, Druids, Shamans, Clerics

Clan Dromoka

Dromoka is one of the five elder dragons of Tarkir. She is a robust, ankylosaur-like beast, well protected by scaly armor, and can breathe searing beams of light. She is a patient, merciful leader, but in battle, she does not hesitate to unleash her breath weapon to obliterate those who dare stand against her.

Under the Elder Dragonlord Dromoka, the Abzan name was forgotten, and the group became known as clan Dromoka. The Dromoka were a true community, dragons and desert survivors bound together by their common allegiance to their devoted dragonlord. The dragon scalelords fostered trust among their subjects, while the other clans spent their time quelling rebellions. This was achieved by separating the children from their parents and raising them communally, instilling obedience to the dragons into them from an early age. Dragons sat on the top of extended adopted families that were organized meritocratically, offering everyone a place. The dragons even offered their scales to distinguished humanoids as protection. The only exceptions were those who wanted to reinstate the kin-tree traditions, who were regarded as heretics and hunted.

Dromoka herself traveled between the various aeries, inspecting them for weakness. If possible, she would attempt to rectify the situation; if not, she would summarily devour the weak link.

• Main races: Hounds, Birds, Humans, Dragons
• Main classes: Soldiers, Archers, Scouts, Warriors

The Alacrian Quickbeasts

The Alacrian Quickbeasts is a racing team from Alacria that competes in the Ghirapur Grand Prix on Avishkar.
Working in rider-and-steed teams, the Alacrian Quickbeasts are unique among the competitors of the GGP in that they are a team of racing partners, not just master and beast.

Quickbeasts are huge winged creatures from Alacria, a plane connected to Avishkar by a perennial Omenpath. Fueled by a diet of aether, Quickbeasts are capable of startlingly quick, sustained movement and propelling themselves and their riders at high speeds across varied terrain for days at a time between feedings. They are intelligent creatures, ancient and valued by the riders they choose to partner with. Often they are regarded as the souls of the city districts across Alacria, whose honor and legend they inherit from the Quickbeasts that sired them. Riders must pass through extensive schooling and training before they can mount a Quickbeast, and even then, only with the consent of the beast. When this happens, they become bound and occupy the two aspects of their district's legend together.

The team of Alacrian Quickbeasts present in the second Grand Prix represents the best of Alacria's districts and race for the collective honor of their homeworld. They are led by Caradora and Lagorin, a rider and Quickbeast who were not originally bound together but have been forced into a racing pair by tragic circumstances back home.

• Main races: Humans, Leonin, Beasts
• Main classes: Mounts, Knights, Pilots

The College of Vigorbloom

Vigorbloom is the School of Invasive Healing at Hexhaven University on the Echoverse version of Arcavios. It is aligned and the counterpart of Witherbloom. The founder of the school is TBA.

Invasive healing is a somewhat intimidating combination of words, but it suggests to us that lifelink could play quite a big role, as slamming creatures into your opponent to gain life could be seen as invasive.
Not much else is known yet, due to the set and story not being released yet.