The Golgari Swarm

The Golgari Swarm is the embodiment of life and death. The teeming masses of the Swarm believe that life and death are both natural and equally essential.
To them, life and death are natural elements of a cycle with no intermediary break.

Growth is power that comes slowly, but it is also ruthless and inevitable, and this makes growth a key virtue of the Swarm's power. With their dead being planted and regrown as plant zombies, their reanimation magic has made the Golgari the largest Ravnican guild.
Much like a swarm of insects, the Golgari often seem to behave more like a single organism than as a group of individuals. The whole Swarm is driven by a primal instinct to survive and reproduce.
The Golgari are one of if not the largest food suppliers on Ravnica, serving a cheap, plentiful, nutrient-packed gruel to those who can't afford expensive meat or magically-generated produce.
The Golgari Swarm consists of many sub-factions, each with its agenda. Their revered parun is the legendary necromancer Svogthir, the "god-zombie".

Golgari decks dredge the graveyard for a good beater.

• Main races: Beasts, Elementals, Elves, Insects, Gorgons, Saprolings, Wurms, Oozes, Zombies
• Main classes: Druids, Shamans

The College of Witherbloom

Witherbloom is the College of Essence Studies at Strixhaven University on the plane of Arcavios. It is black/green aligned and uses Pests as mascots. The founder of the college is the elder dragon Beledros Witherbloom.

Witherbloom is the natural sciences college of Strixhaven. Their magic centers on life gain. They draw power from the essence of living beings, whether that means enhancing nature or exploiting it.
Witherbloom mages are most at home riding zombie crocs, picking herbs for potions, and hanging out in their swamp, making grim jokes.

The Witherbloom college has its students draw power from opposing and rival forces, with the best example being life and death - their conflict is based on whether existence is driven by the propagation of the species (green magic) or escaping the clutch of death (black magic).
These spells are crafted using natural components like the essence of living creatures or herbs. While many students use their powers for the greater good - like defending the ecosystem from pollution and/or harmful forces - the college motto of "Get Your Hands Dirty" certainly applies to students who use their abilities for death and corruption.

• Main races: Dryads, Humans, Pests, Treefolk, Trolls, Vampires, Elves, Bears
• Main classes: Warlocks, Druids

The founder:
Beledros Witherbloom

Beledros Witherbloom is one of the five elder dragons from Arcavios that founded Strixhaven. The Witherbloom College is named in her honor. She is a master of the forces of life and death.

She is a quiet sort, not one to insert herself into a conflict unless necessary. She is endlessly patient, an observer and a thinker, aware of when silence and mystery will serve her subjects better than precise answers.
She has a peaceful relationship with life and death, and neither mourns nor shies away from the latter.

The Speedbrood

The Speedbrood is a racing team of alien insects and arthropods from an unknown plane that competed in the Ghirapur Grand Prix across Avishkar, Amonkhet and Muraganda.

The Speedbrood is an odd team of racers from a plane with an untranslatable name who came to race the Grand Prix for similarly untranslatable reasons, much to the excitement of the Avishkari press.
To an individual, they were a gregarious presence in the garages of the Grand Prix, fond of polytonal communal singing, tea brewing, and fine textile trade.
The Speedbrood are nocturnal, restless unless they are racing, and always ready to talk — even if neither party can comprehend what the other is saying.
They wear masks and spiked, black leather clothes, have fire-edged claws, and use fire-spitting staffs as weapons.

• Main races: Insects
• Main classes: Druids, Pilots, Assasins