Spoiler: Information
This is a project of mine to fix the Way of the Four Elements monk. My personal setting puts a lot of emphasis on the four elements as fundamental building blocks of the world. The Four Elements monk would therefore, logically, be a nice, flavorful fit for the setting. Mechanically, however, it leaves a lot to be desired. This is my attempt to fix the poor, maligned archetype and breathe a little life into it.

Please note that this is at present a work-in-progress. I have yet to come up with a good capstone for the class, so any ideas, as well as critique of the remaining class features, would be lovely.

Fist of the Four Elements
You follow a monastic tradition that teaches you to harness the elements. When you focus your ki, you can align yourself with the forces of creation and bend the four elements to your will, using them as an extension of your body. Some members of this tradition dedicate themselves to a single element, but others weave the elements together.

Many monks of this tradition tattoo their bodies with representations of their ki powers, commonly imagined as coiling dragons, but also as phoenixes, fish, plants, mountains, and cresting waves.

Elemental Attunement
Starting when you choose this discipline at 3rd level, your dedication to the four elements allows you to bend them to your will. You gain the control flames, gust, mold earth, and shape water cantrips, if you don't know them already. Additionally, you can spend 1 ki point to cast chromatic orb without expending material components. Wisdom is your spellcasting ability for these spells.

Elemental Devotion
Beginning at 6th level, you gain the ability to more fully align your mind and body with the four elements. Whenever you take a long rest, choose one damage type from the list of acid, cold, fire, or lightning. Until your next long rest, you have resistance to that damage type, and whenever you deal damage of that type you add your Wisdom modifier to the damage roll.

Elemental Form
At 11th level your body is suffused with elemental energy. As an action, you can transform into an elemental form, altering your appearance and enhancing your abilities. While in elemental form, you gain a fly speed of 30 feet (which can be increased by your Unarmed Movement feature), and your unarmed strikes and monk weapons deal an additional 1d10 damage of the type from your Elemental Devotion feature, but you become vulnerable to the type of damage opposed to the type you selected, as shown on the Opposing Damage Types table.

Type Opposing Type
Acid Lightning
Cold Fire
Fire Cold
Lightning Acid