THIS SITE IS INCOMPLETE
Due to the nature of how many things go into making a Party Member, I will only go over the core aspects of very specifically Party Member related stuff. You still need skills, weapons, dialogue, all of that, I'm just not including them since they are detailed elsewhere.
This is a list of the files you will need for a party member to function in OMORI.
Walking, Climbing, Swimming, and Running sprites
Battle Faceset
Save Menu Faceset
This is the Actors tab, which is where all our Party Members are stored. I'll break down everything here.
Name: Self-Explanatory
Class: This is more of an RPG Maker holdover. Every Party Member has their own Class.
Levels: DW Characters cap at 50, RW Characters cap at 1.
Character: This is more of a fallback as movements are coded into a Common Event, but this will be the walking sprites if that Event is not run.
Traits: Various Effects the Party Member will always have. This is mainly just State Resistances in the Actors tab. Everyone besides Omori resists tier 3 emotions, and Omori resists Afraid.
Notes:
<BattleStatusFaceName: faceset> The Faceset the character uses in Battle.
<FearBattleFaceIndex: #> Normally used by Sunny, if the control variable Neutral Face is turned on, the Party Member's neutral face will be changed to the one specified here.
<BattleStatusIndex: #> What corner they are displayed in Battle. 0 for Top-Left, 1 for Top-Right, 2 for Bottom-Left, 3 for Bottom-Right
<MenuStatusFaceName: faceset> Used by RW characters. Sets the face used in the save menu. Must be a 375x125px image of their neutral row.
The rest of the BattleCommandList code can and should be copypasted, with the id for the skill being replaced with the Party Member's basic attack.
This is the Classes tab, which is where all our Party Members' stats are stored. I'll break down everything here.
Name: Self-Explanatory, doesn't show in game though.
Parameter Curves: This is how the leveling will scale for a character. It looks like the devs manually set each level stat, which I think is crazy. You can use the Generate curve button and set the stats as you like there. They will make you input the stat for level 99, even if OMORI caps at 50, so just put double of the level 50 stat. And after it's done generating you can make adjustments if you want.
Skills to Learn: Self Explanatory. Make sure that the Follow-Up checks are added to the list of learned skills.
Traits: Various Effects the Party Member will always have. This is mainly equipment types in the Classes tab. Everyone is assigned the POWER OF FRIENDSHIP skill type and CHARM Armor type. And each character gets their own weapon type. In case you're wonder what KEL type armor is, it's RW Kel's pet rock.
Element Rate: A percentage based multiplier on the damage taken from the element listed. This is used mainly for Emotions.
*Debuff Rate: Changes the probability that a skill or item will debuff the listed stat.
*State Rate: Changes the probability that a skill or item will inflict the listed state.
State Resist: Become immune to the listed state.
Parameter: A percentage based multiplier on the listed stat.
Ex-Parameter: A percentage based adder on the listed stat.
Sp-Parameter: A percentage based multiplier on the listed stat.
Attack Element: Adds the listed element to any skills used. Mainly used for Emotions.
*Attack State: A percentage based chance that an attack will add the listed state.
*Attack Speed: A speed boost added to any skill used.
*Attack Times +: Repeats the skill used. So +1 makes the skill happen twice.
*Add Skill Type: Adds the listed skill type to the available skills. This doesn't really apply to OMORI
Seal Skill Type: Seals use of the listed skill type. Only really used by afraid.
*Add Skill: Learn the skill listed. This is done through troop events in OMORI.
*Seal Skill: Seals use of listed skill. Works fine it's just not used in OMORI.
*Equip Weapon: Unlocks the inputted weapon type. This would allow for characters to equip each other's weapons if out of battle.
*Equip Armor: Unlocks the inputted armor type. All of OMORI's charms except for FA Kel's Pet Rock are the same type.
*Lock Equip: Locks the inputted equipment type. This means you can't change your equipment while the state is active. This is used by all of Omori and Sunny's weapons.
*Seal Equip: Seals the inputted equipment type.
*Slot Type: Meant for dual-wielding. Doesn't work in OMORI.
*Action Times +: A percentage based chance that an actor will execute a command a second time. These can stack.
*Special Flag: Applies effects that don't work in OMORI.
*Collapse Effect: Determine the death animation. Doesn't work in OMORI. That is handled in the enemy Notes tab.
Party Ability: Adds a party wide ability. Only Gold Double and Item Drop Double work and only Gold Double is used.
Movement Graphics for OMORI's Party Members are done through 3 Common Events, Graphics Base, Graphics Climb, and Graphics Swim.
Luckily, all of the cases that are in these events are labelled in Code Comments, so all you have to do is add another script under the main one to add your party member. The format looks like this.
◆Script:var bwalk = { name: 'DW_BASIL', index: 0 }
: :var brun = '$DW_BASIL_RUN%(8)'
: :
: :$gameActors.actor(5).setMovementGraphics(bwalk, bwalk, brun);
The only parts you have to change are the variable names, so that there is no duped variables, the images referenced, and the index for the walking sprite.
The index is done the same as every other image in OMORI, but it refers to the set of movement sprites, not any individual sprite.