A friend of mine will be hosting a game soon. Another friend of ours wishes to play a homebrew class he made up, as he was unsatisfied with the way 5e had no suitable (in his opinion) ways to do something similar to the Beguiler (from, I believe, 3.5).
What he proposed was, in my opinion quite powerful, but I don't wish to simply deny him the opportunity to adopt a play style that 5e's classes don't support especially well, but I find it difficult to rebalance his class in a more suitable way.
Hence my question: How should this homebrewed class be made into something that will not unbalance the game?
Hit Dice: 1d8
Hit Points at 1st Level: 8 + your Constitution modifier
Hit Points at Higher Levels: 1d8 (or 5) + your Constitution modifier per Beguiler level after 1st
Proficiencies (in addition to proficiencies provided by race / background).
Armor: light armor
Weapons: simple weapons, hand crossbows, rapiers, short swords
Tools: thieves' tools
Saving Throws: Dexterity, Intelligence
Skills: Choose three from Acrobatics, Athletics, Arcana, Deception, Insight, Investigation, Perception, Persuasion, Sleight of Hand, and Stealth.
Spells come from the Sorcerer and Rogue(Arcane Trickster) spell lists with some restrictions.
You have full access to all Illusion and Enchantment spells. The rest must either enhance your own abilities, stealth, or be of some utility for a skulk. (DM approval right now; will make actual list when able.)
At 1st level, you know four cantrips of your choice from the Beguiler spell list. You learn an additional Beguiler cantrip of your choice at 4th level and another at 10th level. The only damaging cantrip allowed is poison spray.
You regain all expended spell slots when you finish a long rest.
Spells Known of 1st Level and Higher
You know two 1st-level spells of your choice from the Beguiler spell list. You learn an additional Beguiler spell of your choice at each level except 12th, 14th, 16th, 18th, 19th, and 20th. Each of these spells must be of a level for which you have spell slots. For instance, when you reach 3rd level in this class, you can learn one new spell of 1st or 2nd level.
Additionally, when you gain a level in this class, you can choose one of the Beguiler spells you know and replace it with another spell from the beguiler spell list, which also must be of a level for which you have spell slots.
Intelligence is your spellcasting ability. (Normal spell casting rules apply).
You can use an arcane focus (per CH 5 of the PHB) as a spellcasting focus for Beguiler spells.
At 1st level, pick a Beguiling Style to focus on how you will misdirect and mystify your opponents. This choice grants you features when you choose it at 1st level and again at 6th, 14th, and 18th level.
At 2nd level, choose two of your skill proficiencies, or one of your skill proficiencies and your proficiency with thieves' tools. Your proficiency bonus is doubled for any ability check you make that uses either of the chosen proficiencies.
At 11th level, you can choose two more of your proficiencies (in skills or with thieves' tools) to gain this benefit.
As all beguilers are tricksters of some kind they learn how to take advantage of openings in opponents' defenses and lapses of concentration, or even to further their skill in subtlety. To this end, there are several tricks they learn to use with their spells. These effects are only applied when the target has an enemy other than you within 5 feet and that enemy is not incapacitated, or when the target has disadvantage.
At 3rd level, you gain the benefits of the sorcerer's Subtle Spell Metamagic option on all spells, removing the Verbal and Somatic Spell components of those spells.
At 9th level, you gain a +2 to the spell save DC check for your spells.
At 15th level, when you release a spell with duration: concentration it persists for 2 rounds after it is released up to the maximum duration.
At 20th level, you overcome all spell resistance.
Ability Score Improvement
(Normal). If your DM allows the use of feats, you may instead take a feat.
Beginning at 10th level, when you are subjected to an effect that allows you to make a Dexterity saving throw to take only half damage, you instead take no damage if you succeed on the saving throw, and only half damage if you fail.
By 17th level, you have acquired greater mental strength. You gain proficiency in Wisdom saving throws.
With a flair for twisting the minds of others you learn to delve into the minds of others. Twisting their thoughts and dreams to your whims.
At 1st level you gain telepathy out to a range of 100 ft to a single target at a time so long as they understand a language.
At 6th level, you may attempt to read the surface thoughts of the person as with the spell detect thoughts.
You may use this ability 1 time per long rest for every 5th level after 6th.
At 1st level you gain expertise in one of the following skills: Deception, Insight, Intimidate, or Persuasion.
At 6th Level you gain the ability to use suggestion as in the suggestion spell, but the duration is 2 hours +20 minutes per level or until the task is done instead of concentration. You can’t use this feature again until you have completed a long rest.
At 14th level you may designate a creature of size Large or smaller that you are attempting to charm to be charmed with Duration: Permanent. You may only have 1 being permanently charmed at a time; if you attempt to permanently charm another being, the first stops being charmed. The permanent charm also breaks if the Mindbender's allies attack the permanently charmed being. Dispel magic, however, has no effect when attempting to remove the permanent charm.
You may permanently charm an additional being at levels 17 and 20.
At 20th level you may designate a person or creature you are attempting to Dominate to be dominated with duration: Permanent. You may only have 1 being designated as a Thrall at a time. Additionally the maximum Challenge Rating for the thrall is equal to your level -5.
Pulling material from the plane of shadows, your illusions are real, to an extent. For those who fail to peer behind the veil that which they see is reality, yet those whom are not fooled still see the stuff of nightmares.
At 1st level, if you do not have darkvision already, you gain Darkvision out to 60 feet.
At 1st level, you learn the minor illusion cantrip. In addition, it may create shadow material equipment and weapons. A created weapon does 1d8 damage. This increases to 2d8 at 5th level, 11th level (3d8), and 17th level (4d8). This includes bolts and arrows but only 20 may be made at a time. When the illusion is seen through it is shown to be made of shadow material instead of becoming faint.
At 1st level, you gain the ability to cloak your form in shifting shadows. This cloak is impenetrable by darkvision, but you may see though it as if it were not there. Any being who can see through magical darkness or does not rely on sight is immune to the effects of this ability. It allows the user to make Stealth checks to hide as though concealed; however, a shadowy outline is visible unless further hidden (shadows, breaking line of sight, etc). This ability imposes disadvantage on attacks against the cloaked individual by those who fail their Perception check to see through the cloak. This ability cannot be used in daylight.
At 6th level level the illusion spells silent image, major image, and programmed illusion may be used to recreate spells from the Evocation and Conjuration schools. The spells may recreate any Evocation or Conjuration Spell at least 1 level lower than the spell slot used, as long as the spell has some kind of component that may be used in an illusion. This includes lower-level spells cast using higher-level slots but it bars spells such as sending, teleportation spells, demiplane, and contingency. Shadow Crafted spells only last as long as the Crafted spell or the Illusion, whichever ends first.
Shadow Crafting may also conjure monsters you have experienced so long as the total challenge rating is spell level – 3/4th of the slot used. The Conjured creatures have half the hit points they did previously. The maximum number of creatures is 2 and both must fit within the area of the illusion or image. Conjured creatures cannot last for more than 24 Hours.
Of these Shadow Crafted spells, if any creature makes an Intelligence (Investigation) check against the spell save DC or has the spell proven to be an illusion, that creature takes half damage from such a spell (but not creatures). The addition of shadow material, however, causes the spells to be tangible, but prolonged exposure to the material will allow am extra check as it cannot properly mimic the illusory material.
At 14th level, you may control the Shadow Crafted illusions with a bonus action instead of an action.
At 20th level, your illusions are more real. Upon conjuring the illusion, the reality of it is 20% + 1d12 * 10% (30-140% real). This affects spell damage and creature hit points.