What are some fun and creative concepts you can come up with for how the Astral Self Manifests.

Ill start:

‘Warforged Monk who’s Astral Self looks like a Marut’

Kalashtar Monk whose Astral Self looks like a Quori

Tortle Monk whose Astral Self looks like a Dragon Turtle

Kobold Monk whose Astral Self looks like a Dragon

This is a concept I'd love to try out with a Moon Druid, but I think it would work out with an Astral Monk as well:

Either a Kobold whose Astral Form is a dragon or a Tabaxi/Leonin whose Astral Form is an actual lion or a Yuan-Ti whose Astral Arms are constrictor snakes... basically any animalistic race that morphs into their bestial form when entering combat.

I wanted to create an Astral monk with a noble/gentlemanly like astral form. A top hat with masquerade mask for the face. A long coat for the armor. As for the arms, its a body with formal attire and a cane. 

My concept for an Astral Monk was one in tune with the elements. Instead of a more perfect humanoid, his arms would be tendrils of the elements (no change to the damage type). Whips of air and water, blocks of earth, and blasts of fire would form the visuals for his attacks.

Have your astral self reflect your vision of yourself. For example my changeling who's having an identity crisis would have glitchy astral arms that change shape/color in an erratic manner, but when he overcomes that it becomes a more fluid process where the astral arms gently transition from a form to another.

My astral self would look like a giant praying mantis. When activated the spiked arms would lash out to those in the 10 foot range. Second choice, Thri-Kreen :)

With the sailor background, long octopus tentacles that lash out. 

Or large pseudopods and an amoeba-like gelatinous body. 

A Yuan-ti Pureblood whose astral form is an Yuan-ti Anathema.

A Shifter whose astral form is a true Lycanthrope. 

A Simic Hybrid whose astral form is the completed form of whatever animal parts are grafted into them.

A Tiefling whose astral form is an angelic celestial being that signifies their purity despite their fiendish blood.

An ancient wizened elf. Braided and dreaded long voluminous stark white hair. Tanned and weathered leathery skin, uncomfortably long and semi-droopy ears. With a demeanor that is seesawing violently between cheerful and grumpy.

Monk - Astral Self // Cleric - Peace Domain multiclass.

During combat he calmly strolls though combat, decrying the injustices of violent action, while his massive astral claws savagely destroy the enemies around him. Preaching as he strolls, the virtues of non-action and silent resistance as the bodies fall in his wake, never lifting a finger or striking an enemy himself. The blood stained astral talons of his manifested soul-stuff contrasting against the serenity of his quiet demeanor.

Purely visual? I like to think that since it is your astral form, that despite your combat effectiveness being based on wis, your form itself, cosmetically, is actually based in intelligence. Monks with low Int would have rudimentary, only roughly humanoid shaped forms, blobs, tendrils, mallet-like arms, etc. But those with exceptionally high intelligence would instead have intricate, detailed, vibrantly fluctuating forms. Looking like beings of divine geometric patterns or intricate interlaced clockworks, or similarly complex manifestation only a brilliant intellect could conceive and project.

• Peaceful-calm monk with savage claws
• Monk in straight-jacket with massively strong looking arms
• An amputee with spectral replacements.
• Any standard cultist-type with spooky tentacles
• A more martial type with astral weapons, like swords or similar.
• Death-themed character of some variety with actual ghostly minions.
• Cudgel-like arms that sheath over-top your normal arms
• Bookish-monk with constellations of astral energy interwoven into complex shifting patterns

I like the idea of a kenku unfurling brilliant astral wings to use as weapons.

I can't help but envision the "Stands" from Jojo's Bizarre Adventure, so if I made one it would have to be an over-the-top concept like the ones from that show. As for exact looks, I'd have to decide on a character concept first. Definitely gonna be weird, though. 

You know doctor strange’s magic, that’s what I always imagine 

Quote from VanZoeren >>

I can't help but envision the "Stands" from Jojo's Bizarre Adventure, so if I made one it would have to be an over-the-top concept like the ones from that show. As for exact looks, I'd have to decide on a character concept first. Definitely gonna be weird, though. 

 Same here. Honestly for us JoJo fans, Astral Self is just an excuse for us to get to design a sick looking stand and have fun using it to ora-ora our way through goblins :)