What!?
Yup. We can break that multiclass spellcasting chart into tiny pieces. Here’s how.
Step 1
Ok, first some terms.
1. Listcasters
These spellcasters prepare spells from a list, the number being equal to the number of class levels and your spellcasting ability modifier. They are the clerics, druids, and paladins.
2. Memorizers
These are the spellcasters that, as they level up, learn spells. Thy are the bards, eldritch knights, rangers, arcane tricksters, and sorcerers.
3. Oddballs
These are the classes/subclasses with spellcasting potential that don’t go into the chart or act weirdly for another reason. They are warlocks, wizards and 4 element monks.
Step 2
Now for some important information.
(Note: I used the cleric and sorcerer as examples, because they represent their respective term groups well)
These are the pieces of usable information (for the intents and purposes of a overpowered character)
1. “You can change your list of prepared spells when you finish a long rest.”
2. ”You prepare the list of cleric spells that are available for you to cast, choosing from the cleric spell list. When you do so, choose a number of cleric spells equal to your Wisdom modifier+your cleric level (minimum 1 spell). They must be of a level for which you have spell slots
3. “You know two first level spells of your choice from the sorcerer spell list.”
4. “The Spells Known column of the Sorcerer table shows when you learn more sorcerer spells of your choice. Each of these spells must be of a level for which you have spell slots.”
5. ”Aditionally, when you gain a level in this class, you can choose one of the spells you know and replace it with another spell from the sorcerer spell list, which must also be of a level for which you have spell slots.”
6. ”The Spells Known column of the Warlock table shows when you learn more warlock spells of your choice of 1st level and higher. A spell you choose must be of a level no higher than what’s shown in the table’s Slot Level column for your level.”
7. “You determine what spells you know and can prepare for each class individually, as if you where a single-classed member of each class”
8. “You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes half of your levels (rounded down) in the paladin and ranger classes, and a third of your fighter or rogue levels if you have the eldritch knight or the arcane trickster feature. Use this total to determine your spell slots by consulting the Multiclass Spellcaster table.” (Note:The table is the same as a sorcerer spell slot table)
9. “At first level, you know 3 cantrips from the cleric spell list. You learn additional cantrips of your choice at higher levels, as shown by the Cantrips Known column on the Cleric table.”
10. “At first level, you know 4 cantrips from the sorcerer spell list. You learn additional cantrips of your choice at higher levels, as shown by the Cantrips Known column of the Sorcerer table.”
Step 3
Now for the rules lawyering.
1. In the second quote, it is stated that they(the prepared spells) must be of a level for which you have spell slots. That is the only specification.
2. In the first quote, it is stated that the prepared spell list may be changed. Meaning, if one had enough levels in, as an example, cleric, one could choose to have 0 first level spells.
3. In the eighth quote, it is stated that the spell slots of a multiclass spellcaster are determined in a way that lets a, for example, cleric/2 sorcerer/1 have a second level spell slot, which in turn, allows the cleric to prepare second level spells.
4. In the fifth quote, it is stated that a memorizer spellcaster may swap one spell for another spell, with that spell having to be of a level for which the caster has spell slots.
5. In the ninth and tenth quotes, it is stated that at first level in the class (otherwise everyone would get a bunch of cantrips) they get x amount of cantrips. In the table referenced by the eighth quote, there is no column showing how many cantrips a character may learn, meaning a cleric/1 sorcerer/1 gets 7 cantrips, 3 from cleric and 4 from sorcerer.
6. The table referenced by the eighth quote also has no column involving a maximum number of spells for a multiclass spellcaster, and the seventh quote specifies that known spells (cantrips are 0th level spells) are determined separately.
7. In the third quote, it is specifically stated that you know x amount of first level spells. You are stuck with them.
Step 4
Explanations
You should take listcaster spellcasting classes first (if you are going to take those classes). They can change their spell list to grab a high level spell that is on their list later.
4 element monks are unhelpful. They can spellcast, but the way they spellcast is incompatible with normal spellcasting.
Warlocks can help other classes learn spells by going to a high enough level to get decently powerful spell slots, but then going into another spellcasting class, such as sorcerer leaves you to start climbing the multiclass spellcasting table from 1st level.
Wizards act like memorizer spellcasters for gaining acsess to spells, but they prepare spells just like any listcaster.
Both Wizards and Book of Shadows Warlocks can learn spells using gp if they come across either wizard spells, or any spell.
You can take the first level of any memorizer spellcaster at any time, because you get a few first level spells by definition.
Step 5
An Example
Now that we know this, we can make an example character. Let’s call her Sally.
Sally is going to start out as a 1st level paladin. She’ll continue taking paladin levels until she is 6th level. Now she is going to take 14 levels of bard. She has access to 0th through 9th level spells. Because (6/2)+14=17 and 17th level is when we get a 9th level spell slot.
Yup. We can break that multiclass spellcasting chart into tiny pieces. Here’s how.
Step 1
Ok, first some terms.
1. Listcasters
These spellcasters prepare spells from a list, the number being equal to the number of class levels and your spellcasting ability modifier. They are the clerics, druids, and paladins.
2. Memorizers
These are the spellcasters that, as they level up, learn spells. Thy are the bards, eldritch knights, rangers, arcane tricksters, and sorcerers.
3. Oddballs
These are the classes/subclasses with spellcasting potential that don’t go into the chart or act weirdly for another reason. They are warlocks, wizards and 4 element monks.
Step 2
Now for some important information.
(Note: I used the cleric and sorcerer as examples, because they represent their respective term groups well)
These are the pieces of usable information (for the intents and purposes of a overpowered character)
1. “You can change your list of prepared spells when you finish a long rest.”
2. ”You prepare the list of cleric spells that are available for you to cast, choosing from the cleric spell list. When you do so, choose a number of cleric spells equal to your Wisdom modifier+your cleric level (minimum 1 spell). They must be of a level for which you have spell slots
3. “You know two first level spells of your choice from the sorcerer spell list.”
4. “The Spells Known column of the Sorcerer table shows when you learn more sorcerer spells of your choice. Each of these spells must be of a level for which you have spell slots.”
5. ”Aditionally, when you gain a level in this class, you can choose one of the spells you know and replace it with another spell from the sorcerer spell list, which must also be of a level for which you have spell slots.”
6. ”The Spells Known column of the Warlock table shows when you learn more warlock spells of your choice of 1st level and higher. A spell you choose must be of a level no higher than what’s shown in the table’s Slot Level column for your level.”
7. “You determine what spells you know and can prepare for each class individually, as if you where a single-classed member of each class”
8. “You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes half of your levels (rounded down) in the paladin and ranger classes, and a third of your fighter or rogue levels if you have the eldritch knight or the arcane trickster feature. Use this total to determine your spell slots by consulting the Multiclass Spellcaster table.” (Note:The table is the same as a sorcerer spell slot table)
9. “At first level, you know 3 cantrips from the cleric spell list. You learn additional cantrips of your choice at higher levels, as shown by the Cantrips Known column on the Cleric table.”
10. “At first level, you know 4 cantrips from the sorcerer spell list. You learn additional cantrips of your choice at higher levels, as shown by the Cantrips Known column of the Sorcerer table.”
Step 3
Now for the rules lawyering.
1. In the second quote, it is stated that they(the prepared spells) must be of a level for which you have spell slots. That is the only specification.
2. In the first quote, it is stated that the prepared spell list may be changed. Meaning, if one had enough levels in, as an example, cleric, one could choose to have 0 first level spells.
3. In the eighth quote, it is stated that the spell slots of a multiclass spellcaster are determined in a way that lets a, for example, cleric/2 sorcerer/1 have a second level spell slot, which in turn, allows the cleric to prepare second level spells.
4. In the fifth quote, it is stated that a memorizer spellcaster may swap one spell for another spell, with that spell having to be of a level for which the caster has spell slots.
5. In the ninth and tenth quotes, it is stated that at first level in the class (otherwise everyone would get a bunch of cantrips) they get x amount of cantrips. In the table referenced by the eighth quote, there is no column showing how many cantrips a character may learn, meaning a cleric/1 sorcerer/1 gets 7 cantrips, 3 from cleric and 4 from sorcerer.
6. The table referenced by the eighth quote also has no column involving a maximum number of spells for a multiclass spellcaster, and the seventh quote specifies that known spells (cantrips are 0th level spells) are determined separately.
7. In the third quote, it is specifically stated that you know x amount of first level spells. You are stuck with them.
Step 4
Explanations
You should take listcaster spellcasting classes first (if you are going to take those classes). They can change their spell list to grab a high level spell that is on their list later.
4 element monks are unhelpful. They can spellcast, but the way they spellcast is incompatible with normal spellcasting.
Warlocks can help other classes learn spells by going to a high enough level to get decently powerful spell slots, but then going into another spellcasting class, such as sorcerer leaves you to start climbing the multiclass spellcasting table from 1st level.
Wizards act like memorizer spellcasters for gaining acsess to spells, but they prepare spells just like any listcaster.
Both Wizards and Book of Shadows Warlocks can learn spells using gp if they come across either wizard spells, or any spell.
You can take the first level of any memorizer spellcaster at any time, because you get a few first level spells by definition.
Step 5
An Example
Now that we know this, we can make an example character. Let’s call her Sally.
Sally is going to start out as a 1st level paladin. She’ll continue taking paladin levels until she is 6th level. Now she is going to take 14 levels of bard. She has access to 0th through 9th level spells. Because (6/2)+14=17 and 17th level is when we get a 9th level spell slot.