The study of magic is variable, and unique for each wizard.  A written mage is one whose ability manifests itself in preparatory, written magic.  You can compose spells on paper, and such compositions open up a world of possibilities for you and your party.

Your fellow written mages are often devoted to the support of others.  Because they cannot cast in the moment, many written mages dedicate themselves to public service -- things that take time.  Those, like you, who choose a life of adventure can quickly become irreplaceable members of their party.  They support their fellow adventurers with compositions and join the fight from afar, all the while continuing their studies and growing their power each day.

*This subclass is inspired by Melanie Cellier's Spoken Mage book series*

Compositions

A complete composition is made up of a single piece of written parchment.  Any spell can be written as a composition, as long as the caster has access to that spell.  All material components are needed when using the composition, but not when writing it.  Compositions can be used at any time from anyone -- not just the composer -- by ripping the parchment.

Preparing Compositions:  Your magical ability is manifested through spell compositions.  You must create your compositions at the start of each day, or choose to create some of them later in the day.  To create a composition you must spend a number of minutes equal to the spell's level.

Creating Compositions:  Each day, you can write the same number of spell compositions as the spell slots you have available.  For example, at fifth level you can write 4 1st-level compositions, 3 2nd-level compositions, and 2 3rd-level compositions.  Compositions have an expiration date, and can only be used for a number of days equal to 10 - the spell’s level.  This means you must keep track of when each composition was made.

Cantrip Compositions:  Cantrips can be composed infinitely and last indefinitely, as long as you take the time to do so.  Very early on, you have learned to adapt your written study to the fast-paced nature of adventure.  You can spend one action writing a cantrip composition, and you can write up to 60 distributable cantrips over one short rest.

Features

Composition Control

Beginning at 2nd level, you can flick your fingers to create pockets of relative safety within the effects of your compositions.  When you cast a damage spell that affects other creatures that you can see, you can choose a number of them equal to 1 + the spell’s level.  The chosen Creatures automatically succeed on their Saving Throws against the spell, and they take no damage if they would normally take half damage on a successful save.

Stack of Parchment

At 2nd level, you can stack compositions and rip them at the same time.  This allows you to cast a spell during both your bonus action and your action.

Open Composition

At 6th level, you can now write compositions that are directly tied to your own life force, and thus give them more power.  You can spend all of your spell slots over the course of 24 hours in order to write a composition of up to two levels higher than the highest spell slot you can cast.  If the process is interrupted mid-way, roll a d4 to determine how many 1st level spell slots you maintain.

Once per day, you can use a composition of a spell level you don’t have a slot for -- whether you used it up or it is too high of a level -- as long as you have the pre-prepared written composition itself.  Casting the spell will cost you hit points equal to 1d4 x the spell’s level.

Renaissance Writer

At 10th level, you can write a composition from any class’s spell list.  It will, however, take twice as many spell slots as it would to compose a spell of that level from your own class list.  You can also spend two spell slots each time you write any composition to double the number of days that composition can be used.

Energy Mage

At 14th level, you can see the strings of energy that attach each spell to its caster.  Once per short rest, for one action you can attempt to take control of the spell and mould it to your liking.  The spell’s energy cannot be dispersed, it must be given a new purpose.

If the spell being controlled is 3rd level or lower, no ability check is needed to take control.  If the spell is 4th level or higher, make an ability check using your spellcasting ability.  The DC equals 10 + the spell’s level.  On a success, you have now taken control of the spell and can use a bonus action to affect it.  The duration and range of the spell stay the same.