A spell thief is not someone an arcane spell caster wants to meat in a dark alley. As quickly as they are seen they have robed you of all your magic and are now hunting you with your own spells. As they progress they only get better at hunting their target pray of arcane spell casters

Spellcasting

When you reach 3rd level, you gain the ability to cast cantrips. See Spells Rules for the general rules of spellcasting and the Spells Listing for the wizard spell list.

Cantrips

You learn three cantrips of your choice from the wizard spell list. You learn another wizard cantrip of your choice at 10th level.

Spell Slots

You will earn a total of 7 spell points, each spell that is stolen takes up a number of points equal to its level.

 Spellcasting Ability

Intelligence is your spellcasting ability for your wizard spells, since you steal your spells buy using your cunning and quick thinking to rest it from the unsuspecting wizard and Sorcerers.

Spell save DC = 8 + your proficiency bonus + your Intelligence modifier

Spell attack modifier = your proficiency bonus + your Intelligence modifier

Arcane Trickster Spellcasting

Rogue Level	Cantrips Known	Spells Known	— Spell Slots per Spell Level —
			1st	2nd	3rd	4th
3rd	3	0	2	—	—	—
4th	3	0	3	—	—	—
5th	3	0	3	—	—	—
6th	3	0	3	—	—	—
7th	3	0	4	2	—	—
8th	3	0	4	2	—	—
9th	3	0	4	2	—	—
10th	4	0	4	3	—	—
11th	4	0	4	3	—	—
12th	4	0	4	3	—	—
13th	4	0	4	3	2	—
14th	4	0	4	3	2	—
15th	4	0	4	3	2	—
16th	4	0	4	3	3	—
17th	4	0	4	3	3	—
18th	4	0	4	3	3	—
19th	4	0	4	3	3	1
20th	4	0	4	3	3	1

Spell Leach

Starting at 3rd level, you can siphon a single spell from a spellcaster with a precise strike. As a bonus action, after you hit a creature with a melee weapon, you can force the creature to make a saving throw with its spellcasting ability modifier. The DC is 8 + proficiency bonus + your Dexterity modifier. On a failed save or when you touch a willing creature, you gain a 1st level spell slot and a prepared 1st level spell chosen by you from the creature’s known or prepared 1st level spells. At 9th you can steal a 2nd level spell, atr 13th this expanded to 3rd level, and at 17th this again increased to 4th level. The creature loses a the desired level spell slot, but still knows the spell and can use it normally. For the next 8 hours, you have the spell prepared and can cast it using your spell slots. If the creature is not a spellcaster you don’t gain any benefits from this feature. Once you use this feature, you can’t use it again until you finish a short or long rest. The time you can hold a spell is increased as you level up. At 9th its raised to 12 hours, 16 hours at 13th, and 20 hours at 17th level.

Magical Ambush

Starting at 9th level, if you are hidden from a creature when you cast a spell on it, you can treat this as a sneak attack as though you had used a melee or martial weapon.

Versatile Trickster

At 13th level, you gain the ability to distract targets with your mage hand. As a bonus action on your turn, you can designate a creature within 5 feet of the spectral hand created by the spell. Doing so gives you advantage on attack rolls against that creature until the end of the turn.

Spell Thief

At 17th level, you gain the ability to magically steal the knowledge of how to cast a spell from another spellcaster.

Immediately after a creature casts a spell that targets you or includes you in its area of effect, you can use your reaction to force the creature to make a saving throw with its spellcasting ability modifier. The DC equals your spell save DC. On a failed save, you negate the spell’s effect against you, and you steal the knowledge of the spell if it is at least 1st level and of a level you can cast (it doesn’t need to be a wizard spell). For the next 8 hours, you know the spell and can cast it using your spell slots. The creature can’t cast that spell until the 8 hours have passed.

Once you use this feature, you can’t use it again until you finish a long rest.