Ability is Charisma. It can innately cast the following spells, requiring no material components:

At will: detect magic, fog cloud, light

1/day each: feather fall, misty step, telekinesis

Due to your Elven ancestry this trait is less then that of a full blooded Clound Gaint.

Your Strength and Dexterity scores increase by 1. Your Constitution score increases by 4

Your Giant Elf ancestery grants you the constitution of a gaint at the cost of a less then giant strength and less then elven dexterity. 

You have proficiency in the Perception skill.

You retain your keen senses from your Elf ancestry but lack Darkvision due to your Cloud Giant ancestry.

You reach maturity at around age 50 and have a average lifespan of 500.

You physically mature slower then a Elf but live longer then a Cloud Giant.

Neutral

Alv Jotun's are almost always neutral in one way or another. There Elven half pulls them in a chaotic direction whilst there Cloud Giant half stretches them both ways, either good or evil.

Alv Jotun's range from between 10 and 12 feet tall and have athletic builds.
You weigh between 800 and 1000 lbs.
Your size is Large.

Your physically resembles that of a double sized half elf with skin hues of tan, gray, or blue. 

Your base walking speed is 40 feet.

Your elven nimbleness combined with your giant size results in maximum foot pace.

You can speak, read, and write Elvish, Giant, and Common.

Alv Jotun's are tolerated in Elvish and Human societies. Cloud Giants are more selective with who they let into there clans. Alv Jotun are more at home in there own small family tribes but take there ancestry seriously. Where you came from is your identity.