Way of Alteration

Monks of the Way of Alteration are adaptable and have two distinct forms, which they involuntary take depending on the time of day. During the light part of the day, when the sun is still out, they've embraced a more serene state of being, but on the opposite side of the spectrum, the darker part of the day, when the moon shows up in the sky, is when they become more aggressive, impulsive and chaotic. It is important to acknowledge that despite those differences in behavior, they're still one and the same person.

Luna & Sol

Starting when you choose this tradition at 3rd level, your unarmed strikes deal radiant damage during the day and necrotic damage during the night, instead of the usual bludgeoning damage. In addition to all of that, you unlock two new abilities, to which if you decide to use one of them, you must finish a short rest before you are able to use either one of them again.

Day - By spending 1 ki point and as an action, each creature of your choice that can hear you within 30 feet of you regain hit points equal to 2d4 + your wisdom modifier (minimum of 1) if it has no more than half of its hit points. When you use this feature as your action, it counts as making an unarmed strike with the attack action for the purpose of martial arts and flurry of blows.
Night - If you are below half of your maximum hit points, you can spend 1 ki point to use your action to gain temporary hit points equal to your wisdom modifier + your proficiency bonus + your monk level. When you use this feature as your action, it counts as making an unarmed strike with the attack action for the purpose of martial arts and flurry of blows.

Pigeon Versus Bat

Also at 3rd level, you gain two extra bonuses for both your day and night form respectively.

Day - The day keeps your mind sound and stable. You gain resistance to psychic damage.
Night - You have superior vision in dark and dim conditions. You can see in dim light within 120 feet of you as if it were bright light, and in darkness as if it were dim light.

Game Changer

At 6th level, you learn two essentially useful combat abilities that can turn the tide of a battle, when you use one of them, you must finish a short rest before you can use either one of them again.

Day - When you hit a creature with your unarmed strike, you can choose to spend 1 ki point and deal extra radiant damage of 2d6 + your monk level. Then if the creature is Large or smaller, it must make a constitution saving throw against your ki save DC or become prone.
Night - When you hit a creature with your unarmed strike, you can choose to spend 1 ki point and deal extra necrotic damage of 2d6 + your monk level. Then if the creature is Large or smaller, it must make a constitution saving throw against your ki save DC or become blinded until the end of your next turn.

Metamorphosis

Beginning at 11th level, you can spend 1 ki point to switch between your day and night mode as an action for an hour once per short rest.

Balance

When you reach 17th level, you get two new options in battle, and when you use one of them, you must finish a short rest before you can use either one of them again.

Day - You can spend 3 ki points and use an action to create a shimmering sphere of light centered on you with a 15 feet radius for a turn, then you choose up to 5 creatures inside the sphere which are to be affected by it, they roll a constitution saving throw against your ki save DC, on a failure they take 10d8 radiant damage and are blinded until the end of your next turn, a successful save would halve the damage taken and not blind them.
Night - You can spend 3 ki points and use an action to shoot a line of corruption up to 30 feet long and 10 feet wide, everyone inside the range of the attack must make a constitution saving throw against your ki save DC, on a failure they take 10d8 necrotic damage and become poisoned for 1 minute, a successful save would halve the damage taken and not poison them.