Gestalt Characters (5e Variant Rule)
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Gestalt characters are an alternative to normal character progression found in 5e. Gestalt rules are akin to multiclassing. However, they are separate, because instead of having levels in multiple classes over time, you gain levels in two classes simultaneously.
Disclaimer: It is recommended to only use these rules for player characters in a one- or two-person party. These rules change the balancing of the game, so consult your DM for his or her approval to use these rules.
When you decide to make a gestalt character, choose two separate classes available to you. Ask your DM for at which character level your party will start at. You gain that number of levels in these two classes. For example, if your DM tells you that you should make a character of 3rd level, you gain the features of the two classes you chose from 1st level to 3rd level. Whenever you gain a level, you gain a level in both of these classes.
When you start to make your Gestalt character, you can still choose only one background and one race to play as. However, since you need to fill more niches, you also learn one additional language, gain proficiency with one additional tool of your choice, and gain proficiency with one additional skill of your choice. Additionally, since you start with levels in multiple classes, you can spend up to 33 points to purchase your ability scores. Alternatively, you can take a new standard array as follows: 15, 15, 14, 13, 11, 8. As another alternative, you can use the class rolling mechanic: roll 4d6 for each ability score and drop the lowest roll.
How the Classes Interact
While powerful, Gestalt characters have some basic limitations on them. You cannot use the multiclass rules, meaning you cannot gain levels in any classes other than the ones you selected to originally make your Gestalt character. Additionally, when you gain hit dice from gaining a level, you only gain the hit dice of one of the two classes of your choice. Likewise, you can have proficiency with only two saving throws at 1st level. You can choose two from any of the saving throws the two classes normally have proficiency with.
When you gain the same feature from multiple classes, such as the Extra Attack feature at 5th level of Barbarian and Fighter, you only benefit from the feature once. However, Ability Score Improvement features are treated differently. Whenever you gain an Ability Score Improvement, you can only increase one ability score by 1 for each one you have. You must gain two Ability Score Improvement features at the same level to be able to choose a feat instead.
In addition to all of this, whenever you gain a Spellcasting feature from both classes you took, choose whichever gives you the highest number of spell slots. You otherwise learn or can prepare the same number of spells and cantrips you would normally have from a given class.
If you chose Warlock as one of your classes and another spellcaster as your other class, your Pact Magic feature works slightly differently. Instead of gaining Warlock spell slots and regaining them on a short rest, you only have the spell slots of the other class you chose and regain a number of spell slot levels equal to your Warlock level whenever you complete a short rest. For example, as a 2nd-level Warlock, you could regain two 1st-level spell slots whenever you complete a short rest, and as a 17th-level Warlock, you could regain any spell slot you choose, to a total of 17 spell slot levels regained. You have a minimum of 1 spell slot when starting at 1st level in this way.
If you chose a class that can cast spells starting at 1st level and another class that gets spellcasting at later levels, you regain up to half your total number of spell slots when you complete a long rest. If the class that can cast spells at 1st level that you chose was Warlock, halve the number of spell slot levels you regain on a short rest (minimum of 1).
If you choose Cleric and Paladin for your two classes, you can use your Channel Divinity options using charges of Channel Divinity from either class, but you regain only up to one expended Channel Divinity use when you complete a short rest. You regain all expended uses when you complete a long rest.
Making a Gestalt Character
Below is a guide that briefly walks a player through the steps of creating a Gestalt character.
First, choose any two classes. Then, choose one background and one race. Then, choose to either build your ability scores from scratch, taking the standard array, or randomly rolling. Make sure to keep multiple ability scores in mind, since you will undoubtedly rely on at least three of such.
Decide at which level you are playing. Then, level up your character to that level. It is suggested that you level your character in the classes you chose one at a time.
Take note of any exceptions to features stated in the rules here before you play.