While most fighters specialize in fighting with their body, the Thaumaturge uses their knowledge to adapt their approach to exploit the weaknesses of their enemies. Rather than hailing from armies or mercenary companies, most thaumaturges have a background in scholarly research, planar exploration, or religious study that then chose to train themselves for battle to use their knowledge for the greater good of defending the world. As such Thaumaturges are equally at home in a library as on the training field. Thaumaturges are almost exclusively self-employed relying on bounties, royal patronage, or their personal wealth to sustain their lifestyle.

Level 3: Exploit Weakness

Starting at 3rd level, choose the type of esoteric lore you specialize in : Divine (Wisdom), Arcane (Intelligence), or Occult (Charisma).

You can use a bonus action to use your esoteric knowledge to identify a weakness of one enemy that you can see within 60 feet of you. The target makes a Charisma saving throw (DC=8 + your proficiency bonus + your lore ability modifier) on a failure you deal additional damage on each of your attacks that hit the target equal to the ability modifier associated with your chosen lore. This damage is of the same type as your weapon, unless your target is vulnerable to a specific damage type in which case it is of a type the target has vulnerability to. This effect lasts for 1 minute or until you use this ability again.

You can use this ability a number of times equal to the ability score modifier associated with your esoteric lore, you regain all uses when you finish a short or long rest. 

Arcane

You gain your esoteric lore from an Arcane source such as study at a wizard school, collecting and studying books of magic, studying and experimenting on extra-planar creatures, apprenticing under a powerful mage, or studying ancient texts.

Divine

You gained your esoteric lore from a Divine source such as a religious order, a celestial mentor or patron, a pilgrimage, religious schooling, or study of druidic secrets. Your lore ability is Wisdom.

Occult

You gained your esoteric knowledge from Occult sources such as membership in a cult, studying lost or banned tomes, exploring strange ruins, an extra-planar patron, travelling to strange planes of existence, or befriending extra-planar creatures.

Level 3: Supernatural Tool

At 3rd level, you learn to create one supernatural tool, which you can use to combat your enemies. Choose one tool from the options below. If you lose your tool or it is damaged/destroyed you can recreate it when you finish a long rest as long as you have access to basic supplies. You must be holding your tool in one hand to use it.

Amulet of Obeyence

Command. As a Magic action, you can cast command as a 1st level spell, this increases to a 2nd level spell at 5th level, 3rd level at 9th level, 4th level at 13th level and 5th level at 17th level. You use your esoteric lore ability as your spellcasting ability for this spell. You can use this ability twice, regaining all uses when you finish a long rest.

(Note: automation for this feature is limited, I have done the best I can.)

Help. When a creature you can see within 60 ft of you makes a d20 test and fails, you can use your reaction to grant them a bonus equal to your esoteric lore modifier potentially turning it into a success. You can use this ability twice, regaining all uses when you finish a short or long rest.

Book of Strange Truths

While holding your Book of Strange Truths you gain the following benefits:

Strange Knowledge. You gain proficiency in two skills or tools of your choice, you can change these skills or tools whenever you finish a short or long rest.

Quick Lookup. While holding your Book of Strange Truths you can quickly look up any creature you target with Exploit Weakness, the target automatically fails the saving throw against that ability (legendary resistance can still cause it to succeed). In addition, you can recharge your uses of Exploit Weakness by spending 10 minutes studying your Book of Strange Truths.

Chalice of Life

The Chalice of Life magically fills itself with purifying water every time you finish a short or long rest, you can use this water to create the effects below:

Restore Life. As a bonus action, you drink from the chalice or feed one willing creature within 5ft of you from the chalice. The target regains 2d10 + 2*your fighter level hit points and becomes immune to this ability until they finish a short or long rest.

Cure Ailment. As a bonus action, you can pour the contents of your chalice over yourself or one creature within 5ft of you. If the creature is unwilling they can make a Dexterity saving throw (DC = 8+your proficiency bonus + your esoteric lore modifier) to avoid all the effects. All spells of 1st or 2nd level end on the creature, as well as any effect causing them to be poisoned, paralyzed, blinded or deafened. Once you use this ability you cannot use it again until you finish a short or long rest.

Eldritch Weapon

When you finish a long rest, you can choose one weapon you are proficient with to be your Eldritch Weapon. While holding your Eldritch Weapon you gain the following benefits:

Energy Weapon. When you equip your Eldritch Weapon you can magically convert it into pure energy. Your weapon gains the Thrown weapon property with a range of 20ft/40ft, and it magically returns to your hand after it is thrown (no action required). In addition, when you equip your weapon choose one of the damage types below based on the source of your esoteric knowledge, your weapon deals that damage type instead of its normal damage until you draw it again.

Arcane = cold, fire, lightning, thunder, or force
Divine = radiant, necrotic, or force
Occult = acid, psychic, or force

Absorb Energy. While you are using your Energy Weapon, you can use a reaction to absorb the same type of energy as your weapon is made from granting you resistance against that damage type until the start of your next turn as long as you retain hold of your weapon. After you have absorbed energy with your eldritch weapon it deals 1d4 additional damage on each attack until the end of your next turn.

Lantern of Revelation

The Lantern of Revelation creates magical bright light in a radius of 20 ft, and dim light for another 20 ft when illuminated (you can choose to have the lantern illuminated or off at the start of each of your turns). Creatures and objects within this light are affected by the following abilities:

Truth Revealed. All spells and magical effects in the area become visible as if all observers are under the effect of Detect Magic. Shapechangers must succeed on a Constitution saving throw (DC=8+ your proficiency bonus + your esoteric lore ability) or revert to their original form. The DC for creatures to successfully Hide while within the area increases by +5. All creatures in the area have disadvantage on Charisma (Deception) checks.

Dispel Darkness. If the light of your lantern overlaps any magical darkness or spell that creates darkness, you can attempt to dispel that spell or magical effect. Roll a d20+your esoteric lore ability modifier. If the total is higher than 10+the spell level or higher than the DC of the magical effect you successfully dispel the spell/magical effect. You can only attempt to dispel one such effect per round.

Magic Wand

You gain a magic wand that you can use to create basic magical effects. When you take the Attack action, you can replace any of your attacks with one of the effects below:

Ray of Magic. Ranged Spell Attack. Range: 120ft, one target. To Hit: your esoteric lore modifier + your proficiency bonus. Damage: 1d10+your esoteric lore modifier damage. The damage type depends on your esoteric lore source:

Arcane = cold, fire, lightning, thunder, or force
Divine = radiant, necrotic, or force
Occult = acid, psychic, or force

Burst of Magic. Range: 60 ft, Area: 10ft radius sphere. Each target in the area must make a Constitution saving throw against DC=8+your proficiency bonus + your esoteric lore modifier, on a failure they take 1d10 damage. The damage type depends on your esoteric lore source (see above).

Mirror Shield

This polished metal shield has been enchanted to repel scratches and dirt ensuring it is always buffed to a surface as smooth and reflective as a mirror. While holding this shield you gain the normal +2 bonus to your armour class and you gain the following two abilities:

Distracting Reflection. As a bonus action you move the shield to reflect the distorted image of your enemy back at themselves distracting them. Choose one creature within 15ft of you, you have advantage on the next attack roll you make against the chosen target.

Deflect Magic. When an enemy makes an attack roll against you as part of a spell, or other Magic action, and misses, you can deflect that attack back at your attacker. As a reaction, you deflect the attack back at your attacker, they must make a Dexterity saving throw against 8+your proficiency bonus + your esoteric lore modifier taking 2d10 force damage on a failure.

Level 7: Scroll Cypher

Starting at 7th level, you can use the Magic action to successfully cast any spell from any scroll without making a skill check regardless of normal requirements to use the scroll.

Level 10: Second Tool

At 10th level, you gain a second Supernatural Tool, you must be holding each tool to use it / gain its benefits.

Level 15: Talisman

Starting at 15th level, whenever you finish a long rest, you can use bits of spellcasting components, alchemical ingredients, holy symbols are other esoteric items to create up to 4 talismans from the list below. Each talisman must be affixed to items of equipment or clothing prior to use and is destroyed upon use or when you finish your next long rest.

Wooden Heart: produces the effect of death ward, is destroyed when the spell ends.

Feathered Wings: Activation: Bonus Action which grants a 30 ft fly speed for 10 minutes.

Fish Scales: Activation: Bonus Action which grants a 30 ft swim speed for 10 minutes.

Crystal Flame: Activation: Reaction to taking fire damage, grants resistance to fire against the triggering effect.

Unmelting Snow: Activation: Reaction to taking cold damage, grants resistance to cold against the triggering effect.

Copper Wire: Activation: Reaction to taking lightning damage, grants resistance to lightning against the triggering effect.

Medusa's Eye: Activation: Reaction to becoming Restrained, ends the restrained condition on you.

Level 18: Master of Esoterica

When you reach 18th level, you have reached the pinnacle mastery of esoterica. You gain the following benefits:

• You no longer have limited uses of Exploit Weakness.
• You learn the designs of all the supernatural tools and can create any one of them over the course of a short rest. You can still only have 2 active tools at a time.
• At the end of each long rest, you can create 1 scroll of a spell of 5th level or lower of your choice from the Wizard, Druid or Cleric spell list, this scroll vanishes after 24 hours.