Way of Blue Magic

The Blue Mage embodies a harmonious fusion of monk-like discipline and the spiritual energy of the monstrosities they face. They possess the extraordinary gift to absorb and permanently learn monster attacks and abilities used against them. 

United by an ethical code, the Blue Mage deftly treads the line between their humanity and the innate properties of the monsters they face. Mindful of the perils in recklessly embracing potent monster traits, they proceed with caution, balancing their power while harmonizing with their inner spirit.

Evolving beyond the boundaries of humanity, they harness the absorbed innate properties, wielding their newfound power with balance and control. This transformation into a monstrosity marks the culmination of their arduous quest, as they embrace their duality. The mesmerizing symphony of power they weave draws from the essence of their foes, a testament to the Blue Mage's unwavering spirit and unique path.

Blue Magic

Starting at 3rd level, as a Blue Mage, you possess the unique ability to absorb and permanently learn monster abilities and attacks used against you. When a creature uses an ability or attack that targets you, you can use your reaction and spend 1 Ki point to attempt to learn it. Make a concentration check with a DC of (8 + Monster's Proficiency Bonus + Monster's Constitution Modifier) or 1/2 the damage taken, whichever number is higher. If you succeed, you learn the ability/attack. Note that using this reaction does not prevent the original ability/attack from affecting you.

Restrictions:

1. You must be the target of the ability/attack to learn it.
2. You must be personally affected by the ability/attack; if you are protected in any way, the ability cannot be learned.
3. You can learn an ability that affects you regardless of whether you succeed or fail the saving throw against it.
4. You cannot learn a Legendary Action

You may learn up to a maximum of your monk level plus your Constitution modifier in powers. If learning a new ability/attack would cause you to exceed this maximum, you can choose to replace an existing one.

Using Learned Abilities Once you've learned an ability or attack, you can use it by spending Ki points. You are proficient in this attack. Ki save DC = 8 + your proficiency bonus + your Wisdom modifier

• Monster abilities: The Ki cost is the difference between the creature's Challenge Rating and 1/2 your Monk level (rounded up), with a minimum cost of 1 Ki points.  These abilities remain as cantrips. Your Wisdom modifier determines the results of these abilities. These abilities cannot be countered or canceled by anti-magic. Recharge mechanics on the absorbed ability still apply. 
• Monster attacks: The Ki cost is the difference between the creature's Challenge Rating and your Monk level (rounded up), with a minimum cost of 0 Ki points.  These attacks remain as cantrips. Your ability modifier determines the attack and damage bonuses, choosing either Strength or Dexterity.

Azure Consumption

At 6th level, the Blue Mage gains Azure Consumption, a powerful ability to absorb the essence of fallen foes. Through a 10-minute ritual, they can attempt to learn a passive or defensive ability possessed by the creature by consuming a part of it, such as its heart or brain. They can use this feature once per long rest.

To succeed in learning the ability, the Blue Mage must make a Constitution saving throw with a DC of 10 + the monster's Challenge Rating. In the event of failure, they become sick, expelling the consumed remains and rendering the opportunity lost.

Each passive ability counts against the total number of abilities the Blue Mage can learn. To maintain the use of these acquired traits, the Blue Mage must expend 1 Ki point for each ability, effectively reducing their available Ki pool. However, these absorbed abilities remain continuously active, unable to be turned off to regain Ki points. If they reach their limit of learned abilities and gain a new one, the Blue Mage has the choice to replace an existing ability or forego the newfound power.

As the Blue Mage harnesses the creature's essence and internalizes their unique abilities, their very form undergoes a transformation to reflect the acquired powers. For example, gaining the +4 natural bonus to armor of the Galeb Duhr manifests in a rocky appearance, epitomizing the fusion of their spirit with the monstrosity they have embraced.

Example Passive Monster Abilities:

Ice Walk (Young White Dragon, CR 10) The dragon can move across and climb icy surfaces without needing to make an ability check. Additionally, difficult terrain composed of ice or snow doesn't cost it extra movement. DC for Blue Mage to learn: 20

Amphibious (Amethyst Dragon Wyrmling, CR 4) The dragon can breathe both air and water. DC for Blue Mage to learn: 14

Magic Resistance (Amnizum, CR 18) The amnizu has advantage on saving throws against spells and other magical effects. DC for Blue Mage to learn: 28

Heated Body (Azer, CR 2) A creature that touches the azer or hits it with a melee attack while within 5 feet of it takes 5 (1d10) fire damage. DC for Blue Mage to learn: 12

Blue Weaving

At 11th level, the Blue Mage can seamlessly weave their learned abilities into combat. When they take the attack action, the Blue Mage can replace one of their attacks with a single-action monster attack they know. Additionally, they can change the damage type of their unarmed strikes or monk weapon attacks to match one from their absorbed monstrous abilities. 

Blue Magic Mastery

At 17th level, the Blue Mage has achieved mastery over their abilities, becoming indistinguishable from the monsters they imitate. The Blue Mage's creature type changes from humanoid to monstrosity (shapeshifter), and they become immune to polymorph and shape-changing effects unless they choose to be affected.

Additionally, you no longer need to spend Ki points to maintain the passive abilities learned from the Azure Consumption feature. You regain the Ki held in this way.