You have completed a ritual that makes your body flexible, like rubber, and have incorporated that into your fighting style. Your limbs can stretch to attack foes outside your normal reach, and eventually you can manually increase your blood flow temporarily to increase your speed, inflate your limbs to deal extra damage, and eventually unlock a secret that can temporarily make you into an unstoppable guardian.

Gum Gum Techniques

• Bloated Blows: Your Martial Arts die for that unarmed strike is doubled. For example, at 3rd level, the unarmed strike damage would be 2d4; at 5th level, the damage would be 2d6. This does not affect unarmed strikes dealt as a bonus action. 
• Sculpted Strikes: Once per turn, you can change the damage type of all of your unarmed strikes to piercing, slashing, or bludgeoning.
• Elongated Limbs: You can give your unarmed strikes an additional 5 foot reach. You can spend 1 ki point to increase the range of your unarmed strikes to a distance of 10 feet. Starting at 7th level, the additional range becomes 10 ft, and you can spend 1 additional ki point to increase this range to 15 feet. 

Rubber Body

You gain resistance to non-magical bludgeoning attacks.

Gear Second

You gain the ability to push yourself beyond your normal limits by using your rubber body to induce a state where your blood pumps harder and faster than a normal being's could.
You may spend two Ki points to enter a state known as "Gear Second" for up to one minute, during which you gain the following benefits:

• Your movement speed doubles.
• Whenever you take the attack option, you can attack three times.
• Attacks of Opportunity are made against you with disadvantage.

When Gear Second ends, you gain a level of exhaustion unless you consume a day's rations.

 

Gear Third

You use the rubber properties to inflate your arm in order to deal more damage on an attack.

Using your bonus action, you may bite into your thumb as an action and expend any number of Ki Points to inflate your arm and enter "Gear Third". While in Gear third, the following effects are applied to you:

• When you enter Gear Third, you gain a pool of d6s equal to the number of Ki Points spent when activating.
  • At 10th level, these become d8s, and at 15th level, these become d12s
• You may only make one attack per turn, maximum.
• When you attack, you expend one die and add that to your normal damage roll. You may spend additional dice from the pool in order to further increase the damage.
• Your AC is lowered by 2.

When you run out of dice, your arm deflates back to normal and all other effects of Gear Third end.

Rubber Body Improvement

You gain resistance to poison damage. You can also move through spaces occupied by large or smaller creatures without suffering a movement penalty.

Slingshot

At 6th level, if you are within 5 feet of an appropriate anchor point, you can use your action to slingshot yourself in a feasible direction by a distance equal to your Unarmored Movement modifier. You can spend 1 ki point to double this distance. What can be used as an anchor point as well as the direction of slingshot are up to DM discretion.

Rubber Body Improvement

You gain resistance to Lightning and Thunder damage. Also, when you take bludgeoning, thunder, poison, or lightning damage, you can use your reaction to gain immunity against that damage type when calculating the damage.

Haki

There are Two main types of Haki, which you can tap into starting at 11th level. Busoshoku Haki allows users to harden their limbs and weapons to either protect themselves or increase their damage output, while Kenbunshoku Haki, which is sixth sense of the world around the user and if trained enough, can even grant limited precognition.

Using Busoshoku Haki, you can do the following:

• If you would be hit by an attack, you may use your reaction to spend 2 Ki points, and increase your AC by your Wisdom Modifier until the start of your next turn. If you do this and the attack misses, you are still treated as having been hit with regards to any non-damaging effects that the attack would have had. You may only use this feature once per short rest.
• When you make an attack, you may use your bonus action to spend a Ki point and add your Wisdom modifier to the damage of all attacks you make this turn. You may only use this feature once per short rest.
• At 16th level, you no longer suffer the once per short rest restriction on Busoshoku Haki abilities.

Using Kenbunshoku Haki, you can do the following:

• You may spend 2 Ki points and take the Dodge action as your reaction. You may only use this feature once per long rest.
  • At 16th level, you may do this more than once per long rest, however the cost increases by 1 for every time you have used this feature since the last long rest.

Bounce

At 11th level, you are a master of manipulation of your unarmed strikes. The maximum range of your unarmed strikes increases permanently by 5 feet, and when you hit a creature with an unarmed strike, you can spend up to 10 ki points to deliver a rebounding strike. The creature must then make a Strength saving throw. On a failed save, the creature is pushed a distance in feet equal to 5 times the amount of ki points spent. On a successful save, the creature is pushed half that distance.

If the creature is pushed into solid object or surface, it takes force damage equal to your monk level. if the creature is pushed into a second creature, both creatures take force damage equal to half your monk level, and the second creature must succeed on a Strength saving throw or be pushed the remaining distance the first creature would have traveled.

Gear Fourth

Entering Gear Fourth requires you to spend 10 Ki points and the entirety of one of your turns. While in Gear Fourth, you gain the benefits listed under the form of Gear Fourth you entered, in addition to 10 special Ki points to use while in Gear Fourth for 1 minute. You lose any remaining bonus Ki points when Gear Fourth ends. When entering Gear Fourth, you may choose the form, from Boundman, or Snakeman.

When Gear Fourth expires, you must make a Constitution Saving Throw equal to 10 + the amount of Ki points you spent while in Gear Fourth, and are incapacitated for 10 minutes if you fail. Either way, you cannot use any of your monk class features requiring Ki points for 10 minutes, due to the immense drain on your body's Ki reserves Gear Fourth requires.

Boundman

 

While Boundman is active, you have the following benefits:

• Your AC becomes 15 + your DEX Mod + your Wis Mod.
• The damage die for your unarmed strikes becomes 1d12.
• You gain a Fly speed equal to your walking speed.
• You are immune to Non-Magical bludgeoning attacks, and have resistance to magical bludgeoning attacks.
• If you attack an enemy that is within 5 feet of you, you may deal an additional 10 damage. You may only deal this damage once per round.

 

Snakeman

 

While in Snakeman, you gain the following effects and abilities:

• When taking the attack option on your turn, you can make up to four attacks instead of one.
• You may now spend up to three Ki points on Flurry of Blows, and make an additional two attacks per Ki Point spent. You may only spend Ki from the pool granted by Gear Fourth on this ability.
• Your movement speed is quadupled.
• Your attacks can home in on enemies. If your attack would miss its target, you may use your bonus action to expend a Ki Point to have that attack continue going and home in on the enemy. At the start of their next turn, the enemy your attack missed makes a DEX save with a DC equal to what you rolled for your attack. On a failed save, they take the full attack.