Archmage

The sky rumbles and flashes as the clouds grow dark and a lone figure gestures from atop a hill. Lightning streaks down from the clouds overhead, striking like the hammer of a god, approaching forces scattering in it's wake.
A woman flicks her wrist from where she calmly sits at her camp, steam rising from her tea. The rushing orcs that had planned to ambush this lone woman fall to the ground in a roaring gout of fire, nothing but charred husks.
A man beckons grandly, cape flying behind him as the parade marches by. A taps his ornate staff on the dragon shaped float which appears to come alive, spraying fire high into the air and roaring with him astride its back.
All of these heroes are Archmages. Figures of renown who wield terrifying amounts of power. Most practitioners of the arcane arts can only dream of reaching such magical heights. Not all Spellcasters are able to become an Archmage, and not all Spellcasters who claim the title truly are. While a powerful spell caster may claim to be an archmage, the title is given only to those truly deserving, decided by a council of other archmages, heads of their respected studies. To be an Archmage is to be an embodiment of the power of magic itself, and avatar of the weave.

High Arcana

At level 21, an archmage is so in tune with magic that they are capable to augment their spells beyond the capabilities of lesser casters. You gain an additional High Arcana at level 23.

Sanctum

 At level 21, most mages finds a place to call their home. Whether you came across a hidden lab while adventuring and claimed it, built a majestic tower that floats through the sky on an amber cloud, a sanctum is a place to conduct research in solitude. Once you have acquired a sanctum, you may spend one week lacing it with your magical energy, attuning to it. While you are attuned to your sanctum, it is treated as your lair, granting you lair actions while in your sanctum. You may teleport to your sanctum once per day for free as per the teleport spell.
Lair Actions

On initiative count 20 (losing initiative ties), you make a lair action to cause one of the following effects; you can't use the same effect two rounds in a row:

1. You choose a 15 ft square area on the ground that you can see within 120 ft. The ground in that area turns into 3 ft deep mud. Each creature on the ground in that area when the mud appears must succeed on a DC 17 Dexterity saving throw or sink into the mud and being restrained. A creature can take an action to attempt a DC 17 Strength check to free themself or another creature within its reach ending the restrained condition on a success when at the edge of the mud pit. Moving 1 ft in the mud cost 2 ft of movement, On initiative count 20 on the next round, the mud hardens and the Strength DC to work free increases to 22.
2. Freezing fog fills a 20 ft radius sphere centered on a point you can see within 120 ft. The fog spreads around corners, and its area is heavily obscured. Each creature in the fog when it appears must make a DC 13 Constitution saving throw, taking 18 (6d6) cold damage on a failed save, or half as much on a successful one. A creature that ends its turn in the fog takes 10 (3d6) cold damage. A wind of at least 20 miles per hour lasts until you use this lair action again or until you die.
3. You conjure two flying swords (Monster Manual pg. 20) which each appear in a spot of your choice that you can see in 120 ft. These flying swords have their hit points maximized, add your proficiency bonus to their attack and damage. These flying swords remain until you use this lair action again or are destroyed.

Arcane Expertise

At level 22, pick one type of magic as your specialty from the following list. You gain the following benefit for the selected magic type.

Abjuration:
You may use Mage Armor as a cantrip. Mage armor bonus becomes 18.

Conjuration:
Whenever you summon a creature you may add your proficient bonus to that creatures AC, Attack and Damage.

Divination:
The range of your divination spells are doubled.

Enchantment:
When a creature makes a saving throw to overcome the effects of an enchantment spell cast by you, you can sacrifice a spell slot or sorcery point to force the creature to fail its saving throw.

Evocation:
When you target a creature with an evocation spell that has immunity to the damage type of the spell, they instead have resistance. If you target a creature that has resistance to the type of the evocation spell cast by you, you ignore their resistance.

Illusion:
When you cast a 1st level or higher illusion spell, you can choose not to regain the spell slot used to cast it when you take a long rest. For as long as you choose not to rain the spell slot, the illusion is considered permanent. If you regain the spell slot the illusion fades.

Necromancy:
When you would be dealt damage by any source, you can redirect that damage to any number of undead under your control, up to their total hit point amount. Any excess damage is dealt to you normally.

Transmutation:
You may create a +3 mundane magic weapon or piece of armor that you are considered proficient with. Once you take a long rest the item fades. You cannot use this power again until you take a long rest.

Chronomancy:

When you cast a spell that has a casting time of 1 action, you can change the casting time to 1 bonus action for this casting. After you use this ability 3 times, you must finish a long rest.

Graviturgy:

When you cast a spell, you can cause gravity to increase with each of your blows. When you make a spell attack against a creature, you can cause it's speed to be reduced by 5 feet until the start of your next turn every time you deal damage to it. Your speed is increased by 10 feet.

Legendary Spell

At level 23, choose a 4th level spell to master. You can use any spell slot of 4th level or less to cast your chosen spell as if it were being cast at 4th level.

Sage of the Arcane

At level 24, when you make an arcana roll and the result is less then 10, you can choose to take 10 in the roll instead. You can attune to an additional item that requires attunement.

Epic Arcana

At level 25, you gain an additional 8th and 9th level slot.

Grand Mage

At level 25, your intelligence, wisdom or charisma increases by 5 and their maximum increases to 30.

High Arcana

Arcane Reach:
Any spell with a range of 5ft or less may be cast up to 60ft.

Mastery of Counterspelling:
You may cast the spell counterspell without consuming a spell slot as if it were a 7th level spell. If the spell is successfully countered in this way, it is reflected back at he original caster. You may use this feature 3 times after which you must complete a long rest before you may use it again.

Mastery of Elements:
When casting a spell that does Fire, Cold, Acid, or Lightning damage, you can change the element type to a different one.

Mastery of Shaping:
When casting a spell that effects an area you may choose a number of 5 ft spots up to your spellcasting modifier to effect within the spells range.

Spell Power:
When casting a cantrip you may sacrifice a spell slot to increase the damage dealt by 1d12 per spell slot level.