Tiefling Traits as presented in the Players Handbook, Page 42:

Aasimar Traits as presented in the Dungeon Masters Guide, Page 286:

Ability Score Increase: Your Intelligence Score increases by 1, and your charisma score increases by 2

Ability Score Increase: Your Wisdom score increases by 1, and your charisma score increases by 2

Age: Tiefling Mature at the same rate as humans, but live a few years longer

Age: Aasimar Mature at the same rate as humans, but live a few years longer.

Alignment: Due to their Fiendish heritage, Tiefling are often Evil, however some reject their heritage, and walk the ambiguous or even righteous path.

Alignment: Due to their Celestial Heritage, Aasimar are often Good. However, some fall into evil, rejecting their heritage.

Size and Height and Weight: Tiefling are built like slightly small framed humans. Your size is medium. If determining Height and Weight Randomly, Subtract 1d4 inches from the of a randomly generated human

Size Height and Weight: Aasimar are built like well proportioned slightly taller humans,  Your Size is medium. If Determining height and Weight randomly, Add 1d4 inches to the height of a randomly generated human

Speed: Your Base Walking Speed

Speed: Your Base Walking Speed is 30 feet

Darkvision: Thanks to your fiendish heritage, you have superior vision in dark and dim conditions. You can see in dim light, within 60 feet of you, as if it were bright light, and in darkness as if it were dim light. You can’t discern colors in darkness, only shades of grey

Darkvision: Thanks to your celestial heritage, you have superior vision in dark and dim conditions. You can see in dim light, within 60 feet of you, as if it were bright light, and in darkness as if it were dim light. You can’t discern colors in darkness, only shades of grey

Hellish Resistance: You have Resistance to Fire Damage

Celestial Resistance: You have Resistance to Necrotic and Radiant Damage

Infernal Legacy: You know the Thaumaturgy cantrip. When you reach 3rd level, you can cast the Hellish Rebuke spell as a 2nd-level spell once with this trait and regain the ability to do so when you finish a Long Rest. When you reach 5th level, you can cast the Darkness spell once with this trait and regain the ability to do so when you finish a Long Rest. Charisma is your Spellcasting ability for these Spells.

Celestial Legacy: You know the Light cantrip. Once you reach third level, you can cast the Lesser Restoration spell once with this trait, and regain the ability to do so when you finish a long rest. Once you reach 5th Level, you can cast the Daylight Spell once with this trait as a 3rd-level spell, and you regain the ability to do so when you finish a long rest. Charisma is the spellcasting ability for these spells

Languages: You can speak, read, and write Common and Infernal

Languages: You can speak, read, and write Common and Celestial

Presented: here a modified version of Tiefling in the Players handbook, based off the sword coast adventures guide

Presented: This Aasimar is based off of the Tiefling Variant in Sword Coast Adventurers

Appearance: Your Tiefling May not Look like the Tiefling described in the players handbook. Choose one of 1d4+1 of the following features

Appearance: Your Aasimar may not look like other Aasimar described in Dungeon Masters Guide. Choose one 1d4+1 of the following features:

Feral: Your Intelligence Score increases by 1, and your Dexterity Score increases by 2, this trait replaces the Ability Score Increase trait.

Mighty: Your Wisdom Score increases by 1, and your Strength Score increases by 2, this trait replaces the Ability Score Increase trait.

Devil’s Tongue: You know the Vicious Mockery cantrip, when you reach 3rd level; you can cast the Charm Person spell as a 2nd level spell once with this trait. When you reach 5th level, you can cast the Enthrall Spell once with this trait. You must finish a long rest to cast these spells once again with this trait. Charisma is your spellcasting ability for them. This trait takes the place of the Infernal Legacy Trait

Angelic Aegis: You know the Resistance cantrip, when you reach 3rd level; you can cast the Sanctuary spell, When you reach 5th level, you can cast the Warding Bond spell once with this trait. You must finish a long rest to cast these spells once again with this trait. Charisma is your spellcasting ability for them. This trait takes the place of the Celestial Legacy Trait

Hellfire: Once you reach 3rd level, you can cast the Burning Hands spell, once per day, as a 2nd level spell. This Trait Replaces the Hellish Rebuke Spell of the Infernal Legacy Trait

Bolstering Presence: Once you reach level 3, you can cast the spell Enhance Ability, as a 2nd level spell, once per day with this trait, this trait replaces the Lesser Restoration spell of the Celestial Legacy Trait.

Winged*: You have large Bat like wings, sprouting from a second pair of shoulders. Behind and slightly above the shoulders of your arms. If you fall while you are conscious, and your speed has not reduced to 0, you may reduce any fall damage you sustain by ½. For you to wear armor or clothing, it must be made to accommodate your wings

At 3rd level, you gain the ability to glide, and negate fall damage while gliding. You can glides long as you can move, and have 15 feet to move horizontally in. Gliding requires 5feet of Descent for every 15 foot of horizontal movement

At Level 5, Your Wings have finally developed full flight capability. Your fly speed is 30 feet

*To use the abilities granted by the winged trait, you must meet the following requirements until you acquire the next ability:

• You must be within your carrying capacity
• Your speed must not be reduced by the armor you are wearing (minimum strength rule on armor)
  

Winged*: You have large bird like wings, sprouting from a second pair of shoulders. Behind and slightly above the shoulders of your arms. If you fall while you are conscious, and your speed has not reduced to 0, you may reduce any fall damage you sustain by ½. For you to wear armor or clothing, it must be made to accommodate your wings

At 3rd level, you gain the ability to glide, and negate fall damage while gliding. You can glides long as you can move, and have 15 feet to move horizontally in. Gliding requires 5feet of Descent for every 15 foot of horizontal movement

At Level 5, Your Wings have finally developed full flight capability. Your fly speed is 30 feet

*To use the abilities granted by the winged trait, you must meet the following requirements until you acquire the next ability:

• You must be within your carrying capacity
• You speed must not be reduced by the armor you are wearing (minimum strength rule on armor)
  

Support Feats (From Xanathar’s Guide to Everything)

Infernal Constitution:
Prerequisite: Tiefling
Increase Constitution Score by 1, to a maximum of 20

You have resistance to Cold and Poison Damage and you have advantage on saving throws against being poisoned

Barbed Hide:
Prerequisite: Tiefling

Increase your constitution or charisma score by 1 to a maximum of 20.

You gain proficiency with the Intimidation Skill, if you are already proficient in it, your bonus is doubled for any check made with it.

As a bonus action, you can cause small barbs to protrude all over your body or cause them to retract. At the start of each of your turns while the barbs are out, you deal 1d6 Piercing Damage to any creature grappling you or any creature grappled by you.

Support Feats (Based on Tiefling Feats in XGtE):

Celestial Constitution:
Prerequisite: Aasimar
Increase Constitution Score by 1, to a maximum of 20

You have resistance to Poison Damage and you have advantage on saving throws against being Charmed Exhausted or Poisoned

Halo of Light:
Prerequisite: Aasimar

Increase your constitution or charisma score by 1 to a maximum of 20.

You gain proficiency with the Persuasion Skill, if you are already proficient in it, your bonus is doubled for any check you make with it.

As a bonus action you can cause your skin emit or stop emitting, an intense halo of light harmful to other creatures. At the start of each of your turns while your halo of light, you deal 1d6 Radiant Damage to any creature grappling you or any creature grappled by you.