This is a fun little topic. These are my general ideas for each character. Since we already have shadow/triumphant skins, we can have these ones be lunacy/lunar skins
Lunar Wilson: Can craft items as long as they've been prototyped. Exclusive items from things like ancient pseudoscience stations have a blood and extra material cost.
Lunar Willow: All fires created by Lunar Willow are lunar fires, which generate no heat/chill and spawns gestalts
Lunar Wolfgang: Mightiness is based on sanity rather then hunger. His sanity would decrease constantly, but he would have a normal stomach.
Lunar Wendy: Standard Wendy perks, but every few days at dusk, Abigail spawns, and chases after her relentlessly until day breaks. Abigail doesn't aggro onto anything else besides Wendy, and drops "Mourning Contempt" if killed, which can be used by Lunar Wendy for craftables relating to pacifying her sister temporarily or using her as normal. (Yes, literally tainted jacob)
Lunar WX-78: Is solar-powered. He has to get an adequate amount of energy from either natural or man-made light. At dusk or in dark areas, he loses energy at a rate, and if he runs out, his stats start decreasing down to something like 30/30/30. Uses lunar shards instead of gears for upgrades.
Lunar Wickerbottom: Starts with a lunar encyclopedia that basically acts as Wheeler's navigadget. She will also fall asleep at night, and will only wake up after taking damage or suffering from starvation. (The hunger rate for sleeping would be removed) After waking up, she will have groggy walk for the rest of the night.
Lunar Woodie: Basically pre-rework woodie with the log meter, but werebeaver doesn't suck your sanity dry.
Lunar Wes: Just give him 1 health point
Lunar Maxwell: Can summon a large number of gestalt workers that generate light and "go into" their designated work objects (chopper goes into a tree and chops, miner goes into a boulder, shoveler literally goes in and out, fighter goes into a mob and does DoT). However, he's constantly hunted by Charlie and she will strike him the moment he is vulnerable to her.
Lunar Wigfrid: Is rabid and starts losing sanity if she hasn't fought and killed a non-nightmare creature within a time span. She also only eats raw or dried meats. In compensation, she has increased movement speed and attack damage while in combat, and shares this bonus with allies when her inspiration meter is filled up.
Lunar Webber: His craftable spider dens are shattered spider dens with a super long web radius. Any mob or object that touches the web turns into its lunar form if it has one. However, he cannot befriend normal spiders since he is shattered himself.
Lunar Warly: His crockpot is now his permanent backpack with four slots. Putting ingredients in it will cause him to start cooking the food, though he has to move around to properly cook the food. After going x steps depending on the recipe's cook time, the dish is added to his inventory.
Lunar Wormwood: Permanently enlightened. Others around him will also be enlightened. When he blooms fully, spawns special moon moths that turn into moon fauna after some time. Starts at half sanity.
Lunar Winona: Has permanent night vision, but the sanity drain for being in the dark is dramatically increased.
Lunar Wortox: Has the ability to capture the souls of nearby dead mobs, and then release them to fight for him. Basically pokemon souls.
Lunar Wurt: Wurt is tired of making kings, so she decides to establish herself as the queen of merms! Every time she slays a unique boss mob, her legend grows, and the stats of herself and befriended merms increase. However, her legendary status will decrease if she attacks another merm or eats non-vegetarian food.
Lunar Walter: Woby is in a permanent big state and will fight like a beefalo with a toggle similar to Abigail. The catch is that Woby and Walter both share the same health pool, but Woby takes reduced damage and Walter isn't afraid of getting hurt anymore.