Way of Absorbing matter

The small goblin in the funny costume smiles as he pokes the soldier in full plate armor, and suddenly the goblin is made of pure metal

A human kneels down, touches his palm to the solid stone underneath, and his body takes up the substance, transforming him to a being of pure rock.

Whatever the utility is, the way of absorption monks learn to use their Ki to become part of a substance. Gaining enhances natural weapons, strength, speed and other physical aspects of them. For one of these monks, extra strength is never far away. 

Shifting matter

Starting at level 3 when you choose this tradition, you gain the ability to absorb the physical properties of matter. Different matter grants different bonuses. You choose yourself if you are encased or transformed into the material, this is only flavor and does not affect the technical aspects

You may spend one ki point to encase your legs, or your arms in a substance you touch as a bonus action. This substance can not be magical, such as the wall of a wall of force. Encasing just the tips of your feet, or just your fists cost no ki. Encasing any part of your body allows you to gain the benefits of growing natural weapons allowing you to choose between slashing, piercing and bludgeoning damage. 

Alternatively you may spend 2 ki points to encase your entire body in a substance you are touching, provided there is enough of it. In order to be fully encased there needs to be your body mass of said substance (DM's discretion) . You can only be fully encased in one material at a time (however your torso and arms/legs can be different materials). If you are fully encased you gain advantage on Stealth checks if you are surrounded by the same material, for example wood in a forest. The benefits are listed in order of: hands/feet, arms/legs and full body

You only gain the resistance benefits of a material when fully encased in it.

Your transformation lasts until you dismiss it, or until you take a rest. At this level, you may absorb common and mundane substances like iron, stone and wood

Wood: you gain spiderclimb, you can fire wooden spikes with a range of 90 feet which deals the same damage as your martial arts, you gain resistance to bludgeoning damage

Stone: you deal double damage to structures made of stone, you gain advantage on athletics checks to lift objects, you gain resistance to slashing, piercing and fire damage

Iron:  you can transform your hands into smiths tools, tinkerers tools and thieves tools, you gain advantage in athletics and you can add your wisdom modifier to any athletic check you make, you gain resistance to non magical physical damage

Absorption advancements

Your powers of absorption has gained a level of advancement. Starting at level 6, the natural weapons you form your fists into can become more advanced, and they now do additional damage.
You gain the ability to use mending, however size limit for you is 5 feet rather than 1.
Additionally your natural weapons now do a bonus damage of your wisdom modifier

lastly you gain the ability to absorb more advanced materials like glass, steel, coal and cloth

 Steel:  your deflect missile can be used against cantrips such as firebolt,  you gain expertise in the Athletic skill (+benefits of iron), you gain a +1 to AC and resistance to non magical physical damage as well as cold, fire, poison and thunder

Glass: you can fire shards of glass with the range of a heavy crossbow, you gain advantage on attack rolls, you are considered invisible if you are standing still, however you have vulnerability to bludgeoning damage (even if its just your arms)

Coal: your ranged throwing attacks deals fire damage, you gain the ability to cast burning hands using 2 ki points, or Aganazzar's schorcherer for 3 ki points, both at their base level. You gain immunity to fire damage

Cloth and leather: you gain the ability to produce whip like tendrils. these have a grappling range of 50 feet and a striking range of 10, you gain a flying speed equal to your walking speed (through making your arms into leathery wings), resistance to bludgeoning damage

Advanced materials

starting at  11th level, you gain the ability to absorb substances who are even more structurally complex and you dont need as much of the material. You now need around 2/3 of your body mass in a material in order to fully become/ be encased in it.

in addition, you may spend a ki point to absorb more of the same material you are encased in, healing some of the damage you have sustained. You may heal 1d10+WIS per 4 ki point you use.

You gain new options for absorption. Like Ice, Quarts and silver

Ice: your dart weapons now reduces the targets movement speed by 5 feet per hit (until the start of their next turn). you gain immunity to cold damage and resistance to fire damage

Quartz:Your dart weapons are now small bolts of lightning, your movement speed is increased by 10 feet,  you gain resistance to slashing, piercing and lightning damage. 

Silver: your melee attacks deal an extra damage die in force damage, you gain the same benefits as iron

 

Material Mastery

Starting at 17th level, your skill with absorption has reached its peak. Granting the ability to absorb forms of energy and volatile materials. these does not have an increment options and can only be done by fully absorbing said energy. tuning into energy cost you 8 ki points. Sources for such energies can often be found in attacks or spells. however absorbing from an attack means you automatically fail the saving throw (if there is any).

You gain the ability to turn into forms of energy, while in energy form, you are immune to the damage dealt by the same energy. All energy forms grants resistance to physical damage.

Lightning: your movement speed is now 80 feet, you can hover. Your unarmed and spike attacks deal lightning damage, and you may spend 4 ki points to cast lightning bolt, for additional ki points you can increase the level of the spell to a maximum of level 6

Fire: you are under the investiture of flame spell, but with a flying speed equal to your walking speed, you can hover

Water: your unarmed strikes now have a range of 10 feet. You gain immunity to magical slashing, bludgeoning and piercing damage, but you also have vulnerability to fire, lightning, cold, thunder, force and poison damage. you have a swimming speed equal to twice your walking speed