Starting at level one, you choose 2 classes. You gain all the level 1 features of both classes. When you level up, you gain a level in both of your classes. you are considered to be the level that both your classes are. For example if you are a Wizard 3 + Warlock 3, you are a 3rd level character. 

Gestalt characters are unable to use the multiclass rule. The two classes you choose at first level are the only classes you are allowed. 

You get the hit dice for both classes every level but add your Constitution modifier only once for each level. 

Example: A Paladin/Sorcerer Gestalt would get 10 + 6 + CON at first level, and 1d10(6) + 1d6(4) + CON every level after 1st

You gain all the proficiencies for both classes. This includes Skills, Weapons, Armor, and Tools.

Additionally, instead of gaining the normal saving throw proficiencies for your classes; you gain proficiency in all saving throws. Any feature that would give you proficiency instead gives advantage in the saving throw.

Your proficiency bonus is normal for your level.

Whenever you gain an Ability Score Improvement (ASI) in both classes, you instead gain an ASI and a Feat.

Note: the ASI in this case can also be a Feat.

You get the spell slots of each Caster separately with the exception of Sorcerer. If either of your chosen classes are Sorcerer, all of your spell slots of 5th level or lower are converted to Sorcery points. The Pact Magic and Natural Magic features are unaffected by the Sorcery point exchange.

If both of your classes have the ability to cast spells, you: 

• choose one of the class' Spellcasting abilities and use it for both classes. 

• use either class' spellcasting foci for both class' spells.

• can cast up to two spells on each of your turns. One with a casting time of an Action, and one with a casting time of a Bonus Action.

Example: A 3rd level Bard/Wizard would choose a spellcasting ability of Intelligence or Charisma, with eight 1st-level spell slots, and four 2nd level slots. If you took Sorcerer for either class you would instead have 28 sorcery points.

You gain all the known spells of both classes; you can cast any spell you know with any spell slot you have of the appropriate level.

You gain all the Cantrips of both classes.

If you have a feature from both of your classes that allow you to Master weapons, you gain one more mastered weapon than you would have before on the class that granted the most masteries, and all mastered weapons now have two additional mastery properties instead of however many they would have had.

If one of your classes is Rogue or Barbarian, you do not gain the additional Mastered weapon. If one of your classes is Monk, your additional Mastered weapon must be Unarmed Strikes, and instead of the extra additional property you gain your special technique.

If your class gains additional mastery properties at later levels, such as a Fighter at 5th level, you gain them on all mastered weapons. If both classes gain additional mastery properties, you gain one as normal and also gain the Specialist Mastery.

If each of your classes calculates their Mastery Save DC's with separate abilities (such as WIS for Monk), choose one and use it for all mastered weapons.

If both of your classes grant you an additional Action, you gain an extra Bonus Action instead of an Action for the second class. You use the feature from the class that has the fewest restrictions for granting that additional Action (such as Bladesinging Wizard's Martial Acceleration allowing the additional action after using a cantrip.)