Spell Thievery

Beginning wizards usually learn about the fundamental structures and formulation of spells, how casters draw power from the world around them and use it to fuel their spells. Spell thieves are wizards that focus on that early training on the workings of spells, deepening their understanding and twisting those concepts in ways that allow them to take power from the spells of other spellcasters.

Deep Arcane Knowledge

When you adopt this tradition at 2nd level, you gain proficiency with Arcana, and you gain advantage on Intelligence (Arcana) checks when trying to recall or understand information about spells or the raw nature of magic in the world.

When you first gain access to a new level of spells at level up, you gain one additional spell of that level to add to your spellbook.

Spell Thievery

Starting at 2nd level, you gain the ability to use your knowledge of spells in a way that lets you siphon a portion of the magic from another caster's spell. As a reaction when another creature casts a spell within 30 feet of you, you can use Spell Thievery to attempt to weaken that spell and take some of the magical energy for yourself. The casting creature must make an Intelligence saving throw against your Spell Save DC, and cannot purposefully fail the saving throw.

If the caster fails, any target of said spell gains advantage on saving throws against that casting of the spell (if the spell allows one). If the weakened spell has a duration other than concentration, that duration is halved.

The stolen spell energy becomes a temporary spell slot that lasts until you use it or until you begin a long rest, fall unconscious, or die. Like temporary hit points, this temporary spell slot is used first when you cast a spell of the matching slot level. The spell slot you create is equal in level to half of the one used by the weakened spell, rounded up (cantrips provide no spell slots, while a 1st-level spell would provide you with a 1st-level spell slot). It must be of a level you can already cast.

If the caster succeeds on the saving throw, the spell is unaffected and you do not gain a spell slot.

You can use this ability again after completing a long rest. You gain a second use of Spell Thievery at 6th level and a third use at 10th level, and all uses are restored after a long rest. The range to use this ability extends to 50 feet when you reach 10th level.

Spell Burglary

Starting at 6th level, you gain knowledge of the counterspellspell. It is always considered prepared, and does not count against the number of spells you can prepare.

In additional, when you cast counterspell and are successful, you may choose to absorb the spell's full magic (instead of just disrupting it) if you have at least one use of Spell Thievery available. Doing so expends one use of Spell Thievery and gives you a temporary spell slot equal to the countered spell's slot level (or the highest spell level you can cast, if the countered spell is too powerful for your current casting abilities).

Spell Piracy

Beginning at 10th level, you can use counterspell to redirect the countered spell to another creature or target, with redirected spell's range starting over from your location. The redirected spell uses the original caster's spell DC or yours, whichever is higher. If your counterspell used a higher level spell slot than the original spell, it is now considered to be of that higher spell slot level.

You can use this ability again after a short or long rest. It cannot be combined with the use of Spell Burglary.

Spell Plunderer

Starting at 14th level, you gain the power to capture a spell and hold it for your own use.

As a reaction when another creature (or object) casts a spell, you can absorb the power and formula for that spell into yourself. The source of the spell must be within 50 feet of you. If the caster is a creature, it must make a saving throw against your Spell Save DC, using its casting ability, and it cannot purposefully fail the saving throw. If the spell's source is an item or object, you must succeed on an Intelligence (Arcana) check with a DC equal to 10 + the spell's slot level.

If the casting creature fails the saving throw (or you succeed on the skill check), the spell does not take effect and you temporarily gain the knowledge and ability to cast that spell. The captured spell must be of a spell slot level that you have access to normally.

When doing so, you gain a temporary spell slot equal the the one used to cast the spell (which can only be used to cast that same spell), and that spell is considered to be prepared by you until you cast it. You use your Intelligence modifier if the temporary spell normally uses Wisdom or Charisma. This temporary spell slot is the first one used when the plundered spell is cast (even if you already had the same spell prepared normally).

If you choose not to cast the plundered spell and it is a spell castable by a bard, sorcerer, or wizard, you can expend it slowly outside of combat (sitting still with your spellbook, components, and inks within reach) while you mentally unravel the workings of the spell and transcribe it into your spellbook (which costs 10 gp per spell level in rare components and inks and takes 3 hours per spell level). Any spell you record in this manner is considered a wizard spell for you. You cannot start a short or long rest while transcribing the spell, as doing so after starting ruins the process.

If not used, the plundered spell (both the temporary spell slot and the knowledge to cast it) fade when you begin a long rest.

You can use this ability again after completing a long rest.