As an undead embodiment of will of Gods of Wisdom, your soul is forever sustained by your divine masters, but your body is temporary and fragile.
You gain +2 to either Intellect or Wisdom ability score, as well as +2 to your Constitution ability score, because your body is sustained and tied together by ancient and powerful magic. Unfortunately, you gain -2 to Strength ability score as you are weak and slow abomination.

You gain Truesight of radius of 60 feet. As an Undead master of Arcane Arts chosen by mighty Kelemvor and Oghma to collect power and knowledge and protect it from selfish entities trying to do evil deeds, you must be able to distinguish truth and lie from one another. Thus, Kelemvor has granted you enhanced vision, allowing you to see everything as it really is.

You gain the Spare the Dying cantrip and you can cast it at will. Once you reach 5th level, you can cast Speak with Dead once a day. Once you reach level 9, you gain the ability to cast Contact Other Plane as ritual once a day. Intelligence is your Spellcasting ability for those spells.

As ascended embodiment of Death and Wisdom, you gain access to certain set of spells allowing you to commune with the dead or your patron, in order to better perform your duty. Kelemvor, as a God - Scribe of Death, has granted you magical insight in the past death, to better understand present and future in form of Speak with Dead spell, while Oghma, Goddess of Knowledge, bestowed you with gift to Contact Other Plane, so you can peek into her libraries to find answers for tough questions. Kelemvor also knows, that sometimes, its better to Spare the Dying, in order to enhance his future Chronicles in the Underworld.

Your walking speed is 25 feet. As undead abomination, which only resides in temporary physical form, since your true strength comes from your spirit, mind and dedication of your service to your masters, you don't need physical speed and strength, your mind is quicker anyway.

You know all Languages you knew in life. You also gain one additional language of your choice.

Kelemvor and Oghma bestowed you with gift of Immortality in form of eternal servitude as neutral, emotionless husk containing immensely powerful soul, hanged in a balance between the world of the Living and the Dead. In order to better perform your duties, you need to be able to communicate freely with everyone and every being that will cross paths with you. Not always this communication will be peaceful, but you can be sure, that you will learn a lot from its outcome.

Ascended Liches or Liches in general, never age. They either feast on the living in order to sustain themselves, or they rely on gods blessing of never ending life for price of eternal servitude. Keeping God's favor may be tricky, but most devoted of their followers can be sure, that their prayers will not be forgotten.

Ascended Lich as a true undead lord of wisdom and power, sustained only by power of his patron as well as his devotion and prowess in magic, is immune to any condition that may affect living beings. Lich cannot be restricted by such things like fear or exhaustion, they have duties of important matter to attend to, to serve their masters to best of their abilities.

You gain resistance to Necrotic Damage and Bludgeoning, Piercing and Slashing damage from nonmagical weapons. You are also immune to charmed, poisoned, exhausted, frightened, paralyzed and poisoned conditions. You also don't need to eat, sleep or breathe. You still need to spend atleast 2h resting during Long Rest to gain benefit of it.

As a Lich you have access to your phylactery, powerful and very durable container that allows you to rejuvenate from ash when your physical form is destroyed. Ascended Liches do not feed souls to their Phylacteries. Also, their rejuvenation is more rapid, since even if their body mus be made from thin air, dust and ash, it must be made swiftly, to make Lich active again, to not displease Kelemvor and Oghma.

When you reach 0 HP your body is immediately turned to ash and your soul is released into your Phylactery, allowing you to make Death Saving Throws as normal and with Advantage.
Additionaly, when you succeed and stabilize yourself, your soul comes back and instantly recreates your body from ash, making you active again and restoring half of your maximum HP. You cannot benefit from this feature again until you finish short or long rest.

Kelemvor and Oghma are benevolent Gods of Wisdom and they sometimes bestow their most devoted and loyal subjects with great power. Once a day, if you are a spellcaster, as an action you may choose any number of fully spent spell slot levels, in any combination which you have access to. Make an Arcana check against DC that equals 10 + sum of all chosen by you spell slot levels. If you succeed, you regain one spell slot for each spell slot level chosen, respectively. Spell slot level's cannot exceed 8 and you may choose up to 3 different spell slot levels only. You have to finish long rest to access this ability again.