The Library

Tbd

Chosen wing

When you choose this subclass you may pick a class spell list, you may learn spells from that list instead of from the warlock spell list. At the end of a long rest you may ready 2 spells from your list of known spells.

Studious options

At 1st level, Once per rest you may use this feature to cast any spell you know or is added to your studies. The spell cast this way can be no more than half the level of your highest level spell slot rounded down.

If the spell is a ritual spell with a cast time of 10min or less you may cast it as an action.

Arcane conduit

Starting at 6th level, Once per long rest, you may hold your action to conduct a spell.
Conducting a spell, when you witness a creature cast a spell, that you are in range of, you may roll contested spell casting. If you succeed you choose a new target or area for the spell.

Transcribe

Beginning at 10th level, As a bonus action you may replace any one of the following, casting condition, damage type, status effect, buff of one spell you are about to cast with that of another spell you know.

spells without concentration can be given concentration, if you do so you may use an action to recast the spell for the duration on the same target. All damage felt this way after the initial casting is halved. 

Entomb

Starting at 14th level,