Level	Proficiency Bonus	Class Features	Cantrips Known	Spells Known	Invocations Known	1st	2nd	3rd	4th	5th
1st	+2	Master's Proxy, Spellcasting	2	1	-	2	-	-	-	-
2nd	+2		2	2	-	2	-	-	-	-
3rd	+2	Eldritch Invocations	2	3	2	3	-	-	-	-
4th	+2	Ability Score Improvement	3	3	2	3	-	-	-	-
5th	+3		3	4	2	4	2	-	-	-
6th	+3	Master Feature	3	4	2	4	2	-	-	-
7th	+3	Indebted Eyes	3	5	2	4	3	-	-	-
8th	+3	Ability Score Improvement	3	5	2	4	3	-	-	-
9th	+4		3	6	3	4	3	2	-	-
10th	+4	Master Feature	4	6	3	4	3	2	-	-
11th	+4	Indebted Hands	4	7	3	4	3	3	-	-
12th	+4	Ability Score Improvement	4	7	3	4	3	3	-	-
13th	+5		4	8	4	4	3	3	1	-
14th	+5	Master Feature	4	8	4	4	3	3	1	-
15th	+5	Indebted Brain	4	9	4	4	3	3	2	-
16th	+5	Ability Score Improvement	4	9	4	4	3	3	2	-
17th	+6		4	10	5	4	3	3	3	1
18th	+6	Ability Score Improvement	4	10	5	4	3	3	3	1
19th	+6		4	11	5	4	3	3	3	2
20th	+6	Indebted Reflexes	4	11	5	4	3	3	3	2

    At 1st level, you have struck a deal with a powerful entity. Your master grants you features at 1st level and again at 6th, 10th, and 14th level.
    This deal is much more personal than a pact, and due to that, your level scales alongside the spellcasting level of your master's.

    The power of your master is a bit more special than most spellcasters. Instead of taking spells from a predetermined list, your master chooses what spell list you get. It may be a custom spell list, or simply a spell list from a pre-existing class. You may have multiple spell lists, if the DM agrees.
Cantrips
    At 1st level, you know two cantrips of your choice from a spell list(s) of your master's choice. At higher levels, you learn additional cantrips of your choice from the same spell list(s), as shown in the Cantrips Known column of the Indebted Servant table.
Spell Slots
    The Indebted Servant table shows how many spell slots you have to cast your indebted servant spells of 1st level and higher. To cast one of these indebted servant spells, you must expend a slot of the spell's level or higher. You regain all expended spell slots when you finish a long rest.
    For example, if you know the 1st-level spell burning hands and have a 1st-level and a 2nd-level spell slot available, you can cast burning hands using either slot.
Spells Known of 1st Level and Higher
    You know two 1st-level spells of your choice from a spell list of your master's choice.
    The Spells Known column of the Indebted Servant table shows when you learn more indebted servant spells of your choice. Each of these spells must be of a level for which you have spell slots. For example, if you are a 5th-level indebted servant, you have four 1st-level and two 2nd-level spell slots.
    Additionally, when you gain a level in this class, you can choose one of the indebted servant spells you know and replace it with another spell from a spell list of your master's choice, which also must be of a level for which you have spell slots.
Spellcasting Ability
    Your spellcasting ability is determined by your master. Your master may be versed in the art of deception, leading you to mimic their charismatic actions. Or your master may be a researcher of the arcane, forcing you as-well to study and memorize the magical art. In addition, you use your spellcasting modifier when setting the saving throw DC for an indebted servant spell you cast and when making an attack roll with one.
    Spell save DC = 8 + your proficiency bonus + your spellcasting modifier
    Spell attack modifier = your proficiency bonus + your spellcasting modifier

    In your eternal servitude, your master has granted you Eldritch Invocations, fragments of forbidden power that imbue you with an abiding magical ability.
    At 3rd level, you gain two eldritch invocations of your choice. When you gain certain servant levels, you gain additional invocations of your choice, as shown in the Invocations Known column of the Servant table. A level prerequisite refers to your level in this class.
    Additionally, when you gain a level in this class, you can choose one of the invocations you know and replace it with another invocation that you could learn at that level.

    When you reach 4th level, and again at 8th, 10th, 12th, 16th, and 18th level, you can increase one ability score of your choice by 2, or you can increase two ability scores of your choice by 1. As normal, you can't increase an ability score above 20 using this feature.

    Starting at 7th level, your master may tap into your senses temporarily. Your master may spend an action and perceive through your senses until the end of their turn. As long as you are on the same plane of existence as your master, your master can use their bonus action on subsequent turns to maintain this connection, extending the duration until the end of their next turn. While perceiving through your senses, they benefit from any special senses possessed by you, and they are blinded and deafened to their own surroundings.
    If your master is willing, you may also spend an action and perceive through your master's senses, following the same rules as above.

    Starting at 11th level, your master may now channel spells through you. When your master casts a spell with a range of touch, they may choose to spend your reaction and have you deliver it instead, if you are willing. You must be within 120 feet of your master for this.
    Additionally, if you are to cast a spell against your master, they have the option to succeed or fail the throw without rolling, and if you cast a spell that requires a saving throw or take half damage, your master instead takes no damage on a success. Additionally, if you heal your master, they receive the maximum healing possible.

    Starting at 15th level, your master may borrow your brain for a bit. When your master concentrates on a spell, they may choose to pass it on to you, as long as you are willing. Your concentration saving throws for spells concentrated on through this feature gain a bonus equal to your spellcasting modifier on your master (For example: If your spellcasting modifier is intelligence, you would use your master's intelligence modifier).
    If you are already concentrating on a spell, you can maintain concentration on both spells simultaneously. You must roll two concentration saving throws to maintain your concentration, and if either one of them fails, you lose concentration on both spells.
    If you have "Focused Casting" or a similar feature, you instead only have to make one concentration saving throw, however you lose your master's spellcasting modifier bonus. You still lose concentration on both spells if you fail the saving throw.

    Starting at 20th level, you gain an additional reaction per turn.
    Additionally, you may use your reaction to grant your master an additional reaction, and vice-versa. This reaction can only be used once per round.

Homebrew Notes

    This is a class I made for a specific character. The idea of this class is that this sidekick entered into a semi-pact with a player character, referred to as a "Master".
    If you use this class, I recommend creating a subclass specifically tailored for the player character that the sidekick would be indebted to. That's the idea that I build "Servant to Gamil" for.