You are a Humanoid for the purposes of being affected by spells and items that require such. Otherwise, realistically, you're basically a sentient cloud.

You are Medium or Small. You choose the size when you select this race.

Your walking speed is 30 feet. While using Cloudshift/Toxic Smog, you gain a flying speed of 15 feet.

As an action, you can reshape your body to give yourself a head, one or two arms, one or two legs, and makeshift hands and feet, or you can revert to a formless, intangible cloud. While you have a humanlike shape, your body becomes tangible and solid to a point and can wear clothing and armor made for a Humanoid of your size.

While using the Cloudshift feature, you gain a flying speed of 15 feet, and can move through other creatures’ spaces as if it were difficult terrain. All of your equipment when you cloudshift falls to the ground in the space that you previously occupied, save for a singular Tiny or smaller item of your choosing, which is stored inside the mass of your cloud. This item can be a spellcasting focus.

You are unable to be damaged by any nonmagical attacks while in this form.

While using Cloudshift, you can still speak, but cannot physically attack or interact with objects outside of using magical means. However, you are also amorphous, and can squeeze through a space as narrow as 1 inch wide, provided you are wearing and carrying nothing.

You may only use Cloudshift a number of times equal to your Proficiency Bonus, which resets on a long rest. Cloudshift lasts for a number of minutes equal to 5 times your proficiency bonus, before you automatically revert back to your humanoid form. You may attempt to stay in the form longer as necessary, but for every 10 minutes spent past your allotted time frame in Gaseous Form, you begin to take a single level of Exhaustion.

At level 11, the limit is removed, and you may remain in this form indefinitely and shift back and forth as you choose. However, in order to Long Rest, you must revert to your humanoid form.

In addition to Cloudshift’s limit removal, at level 11, you gain access to shifting yourself instead into a toxic cloud, separately from your normal shifting.

All rulings from Cloudshift apply, with the addiction and reruling below;

• While in another creature’s space, their vision is impaired and they have disadvantage on attack rolls.
• While occupying the same space as you, the creature must make a Constitution saving throw at the beginning and end of their turns against your spell save DC, or take 3d6 poison/acid damage, player’s choice. The damage changes to 4d6 at Level 17.

You may only use this form 3 times per Long Rest. Each use lasts for 10 minutes.

Due to your nature, your physical form may darken, lighten, or show sparks of electricity depending on your mood. Others have advantage on insight checks and perception checks used to determine what mood you are in.