Genasi

Ravnica's isolation did not prevent it from connecting to the elemental planes. Though this phenomenon is still under investigation, it's no secret that folks with elemental heritage are not uncommon in Ravnica.

Elements of History

Genasi have different abilities and appearances based on their elemental lineage, though some traits are universal. 
Age. Genasi reach maturity in their late teens and live just longer than 100 years.
Size. Genasi run a wide range of builds and body types. Your size is either small or medium, your choice.
Speed. Your speed is based on your size: 25 feet for small or 30 feet for medium.

Air Genasi

Air genasi are associated with elemental air. They typically inherit light blue skin, hair, and eyes from their auran lineage. A faint but constant breeze sometimes accompanies them, tousling their hair and stirring their clothing. Some air genasi speak with breathy voices, marked by a faint echo. A few display odd patterns in their flesh or grow crystals from their scalps.
Child of Air and Sky. You have resistance to thunder and lightning damage.
Mingle With the Wind. You can cast the levitate spell once with this trait, requiring no material components, and you regain the ability to cast it this way when you finish a long rest. Constitution is your spellcasting ability for this spell.
Unending Breath. You can hold your breath indefinitely while you're not incapacitated.

Earth Genasi

Earth genasi are descended from the Plane of Earth. Elemental earth manifests differently from one individual to the next. Some earth genasi always have bits of dust falling from their bodies and mud clinging to their clothes, never getting clean no matter how often they bathe. Others are as shiny and polished as gemstones, with skin tones of deep brown or black, eyes sparkling like agates. Earth genasi can also have smooth metallic flesh, dull iron skin spotted with rust, a pebbled and rough hide, or even a coating of tiny embedded crystals. The most arresting have fissures in their flesh, from which faint light shines.
Earth Walk. You can move across difficult terrain made of earth or stone without expending extra movement.
Merge With Stone. You can cast the pass without trace spell once with this trait, requiring no material components, and you regain the ability to cast it this way when you finish a long rest. Constitution is your spellcasting ability for this spell.
Mold Earth. You know the mold earth cantrip.

Fire Genasi

Elemental fire burns in the veins of fire genasi. Nearly all those descended from the plane of fire are feverishly hot as if burning inside, an impression reinforced by flaming red, coal black, or ash-gray skin tones. The more mortal-looking have fiery red hair that writhes under extreme emotion, while more elemental specimens sport actual flames dancing on their heads. Fire genasi voices might sound like crackling flames, and their eyes might flare when angered. Some are accompanied by the faint scent of brimstone.
Darkvision. You can see in dim light within 60 feet as if it were bright light, and in darkness as if it were dim light. Your ties to the Plane of Fire make your darkvision unusual: everything you see in dim or dark light is in shades of red.
Fire Resistance. You have resistance to fire damage.
Reach to the Blaze. You know the produce flame cantrip. Once you reach 3rd level, you can cast the burning hands spell once with this trait as a 1st-level spell, and you regain the ability to cast it this way when you finish a long rest. Constitution is your spellcasting ability for these spells.

Water Genasi

Water genasi are descended from the Plane of Water. Most water genasi look as if they just finished bathing, with beads of moisture collecting on their skin and hair. They smell of fresh rain and clean water. Blue or green skin is common, and most have somewhat overlarge eyes, blue-black in color. A water genasi’s hair might float freely, swaying and waving as if underwater. Some have voices with undertones reminiscent of whale song or trickling streams.
Acid Resistance. You have resistance to acid damage.
Amphibious. You can breathe air and water, and have a swim speed equal to your walking speed.
Call to the Wave. You know the shape water cantrip. When you reach 3rd level, you can cast the create or destroy water spell as a 2nd-level spell once with this trait, and you regain the ability to cast it this way when you finish a long rest. Constitution is your spellcasting ability for these spells.