Spell Merging^

You may use your down time to research the effect your spells have on the weave to discern a possible way of merging two old spells into a new spell.

Research requires one work week of work and at least 100 gp spent on materials, bribes, gifts, and other expenses.
Typically, a character needs access to a library or sage to conduct research.

After a work week of research, a character makes an Arcana check with a +1 bonus per 100 gp spent beyond the initial 100 gp, to a maximum of +6. In addition, a character with access to a particularly well-stocked library or knowledgeable sages gains advantage on this check.

Arcana Check

1–5 = Spells backfire damaging you, and have a negative effect related to the spells you attempted to merge.
6–10 = You failed to merge the spells, but gained insight into why, your next attempt involving one or both of these two spells will have advantage on the roll.
11–20 = You sucessfully merge the two spells, creating the effect as discussed with the DM.
21+ = You merged the two spells as before, but you also figured out a way to improve upon it, making the spell more powerful than you had previously imagined. (or equally powerful, but faster to cast, or lower level than expected) The precise boon of this will be decided by the DM, though player input is welcome.

It is possibly to create more than a single spell in a week by this process. You may create a low-level simpler version of the spell you made, and a empowered higher level version of the spell.

Any new spells you create, you are entitled to name, and it will have your name somewhere in its name (eg, Tasha’s hideous laughter).
They will be added to a seperate spell list, that will be linked under the Magic page and menu navigation. Spells on this spell list are only known by their creators, or those the creators teach them too. A list of all players who know the spell will be kept on the spells page. Alternatively you may decide you want you new spell to be common knowledge in which case all may learn it and it will be added to both the previously mentioned spell list and the correct classes spell list.

Finally spells created in this manner DO NOT have a spell level, instead they merely have a spell point cost. Meaning you could learn a 14 point cost spell at any level.

Image – http://towerofzenopus.blogspot.com/2014/09/prismatic-spray.html