Abominations live up to two hundred years after the time they were transformed, sustained by the unholy powers that mutated them, before the dark energies fizzle out and the abomination perishes. 

Use one action to transform from one form into the other. As the curse reforms the body with shadowbased magic, transforming in direct sunlight or aother strong (magical) lightsource is not possible. You can also transform as a reaction when damage is afflicted to you. Any damage calculations use your pre-transformed stats.

The Shadows that mutant you grow over your equipment and magically hide it, protecting it from any damage, but also ranters them inaccessible. This includes bags, potions, armor, backpack and your weapon untill you transform out of beastform. These items can not be used, removed, drawn or stolen by you and others.

Everything becomes effectily unequipped, magical items that grant benefits lose ther effect like you dropped the item. The effect of cursed items and other hard to remove effects will remain. While in beast form you are unable to equipp weapons, shields or armor and you cannot drink potions yourself, has your hands are replaced with claws that do not function as fingers, as such actions that would require the use of fingers are not possible. You can however pull levers, throw objects and perform other simple tasks. Actions like swimming or climbing can be performed with claws, but your method is different.

You have the option to drop anything you are holding in your hands, like your weapon, on the ground while transforming to have it uneffected by this.

You revert to your true form if drop below 4 HP, including dying. If you drop below 75% of your max HP, you must succede saving throw of 5 or higher on a d20. If you drop below 50% you must succed a saving throw of 10 or higher on a d20. If you fail a saving throw, you transform to your true form

Your sight goes beyond that of most mortals. These traits have a range of 5 feet in humanoid form or 15 feet your monstrous form. Choose one of the following options:

Tremorsense: You have tremorsense with a range of 5/15 feet.

Ether Sense: You can sense the presence of any creature within 5/15 feet of you that is invisible or on the Ethereal Plane. You can pinpoint the exact location of such a creature if it's moving.

Blindsight: You have Blindsight with a range of 5/15 feet.

Darkvision: You have darkvision with a range of 5/15 feet.

Your AC can never drop below 5 + 1 for every level in any class or + 2 for every barbarian level (A level 3 figher and level 2 barbarian has a total of 12). An AC higher than this number is not effected, you gain no additional bonuses from this trait to armor, but should any effect reduce your AC it will never go lower than this number.

When in beastform this effect is raised to 10 + 1 for every level in any class or + 2 for every barbarian level.

You have the traits of a dangerous creature. These traits only work when you're in monstrous form. Choose one of the following options:

Reacting Blood: Your blood has the ability to react under stress. Twice per short rest your blood can harden under your skin, giving you +3 AC for 2 turns. This effect can beginn right before taking damage. You also can heal 2 HP at any time twice per short rest. These effects can be used independ of each other and independ of your state, even while being unconscious.

Fangs: You have two fangs, with which you can drain blood from a target. As a bonus action, you may make a special bite attack, where your attack modifier is your proficiency bonus, + your Strength or Dexterity modifier. If you hit, you deal piercing damage equal to 1d6 + your Strength or Dexterity modifier, and gain temporary hit points equal to the damage dealt, and you can’t use this trait again until you finish a short or long rest.

Regeneration: You heal 1 HP every 10min. You can regain a total of 2 HP + your level in any class per day. (A level 5 fighter can heal in one day only 7 HP with this trait). You cannot choose when to use this. In order to save leftover Regeneration you must heal to full HP befor Regeneration reaches its cap. Regeneration can only be stopped by reaching max HP or reaching the daily cap. Regeneration will continue even when unconscious or dead, but the daily cap will not reset if you are below 0 HP. Regeneration is the only Apex Predator trait that will continue in humanoid if you are forced out of beast transformation by dropping below your HP threshold or failing a saving throw to stay in beast form.

Stolen Fey Ancestry: You have +4 advantage on saving throws against being charmed.

Chameleon Skin: You have an extra +10 bonus to Dexterity (Stealth) checks if you have not moved during your turn. You lose this bonus if you move through any means, and regain it at the end of your next turn if you spend that turn hiding without moving.

The Curse that runs in your veins boils, making it harder for the Abomination to rest and sleep. You have a 50% chance that a short rest will have no effect, preventing any and all benefits it would have. You will not heal, regrain spell slots or reset any "times per short rest" limits. You also have a 50% chance that a long rest will be counted as a short rest, but a failed long rest will not roll again. Strong Medicine or powerfull magic that helps with resting or calming down can lower the chance to fail a rest to 30%.

You have unnatural abilities, allowing you to hunt your prey. These traits only work when you're in monstrous form, based on what kind of beast the curse appears as. Choose one of the following options: 

Demi-Flight: The Curse takes a bird or bat like form, transforming your body into a hulking creature coverd in feathers or with leathery skin between arms and upper body. As a reaction, you glide, slowing your falling speed to 60 feet per round, and taking no falling damage. Additionally you can always jump 5 feet higher, and 10 feet farther using your mutated arms as an abstract beat of wings. 

Once you reach level 10, your are so used to and skilled with your mutated body that you are able to Fly and Hover using your arms.

Spider Climb: The Curse takes insect like forms, growing small hairs all over your body and smaller extra eyes on your forehead. You can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Once you reach level 10, your are so used to and skilled with your mutated body that you are able to drop onto a target from the ceiling to attack. Any Melee attack can be used as a drop attack. Both you and your target roll 1d20 + Dex. Your target has to match or overcome your roll to dodge your Drop Down. Drop down attacks do not need a dice roll and will always count as the highest possible role for this attack. Targets do not need to be unaware of you, but you must fall at least 10 feet to perform a drop down

Charge: The curse takes a goat, demon or other horned appearence. You can charge a target at double your movement speed, but once you charge you cannot stop or change direction  until you hit something. If you miss your target (dodge or other reasons), you will continue until you hit an obstacle. In case of an open plain or desert, your charge will stop after 3 turns. If you hit a creature after at least 20 feet of charging, you will deal 1d10 + double your streng modifier of damage. If the target you hit rolls an attack dice in its next turn, it will suffer a -5 on this roll.

Once you reach level 10, your are so used to and skilled with your mutated body that you are able to charge at tripel your movement speed and fling a medium or smaller sized creature 15 feet in any direction you like, including up, but not directily into the ground below you. Based on how the fall ends it will take fall damage or damage based on whatever it was flinged into. If the target you hit rolls an attack dice in its next turn, its roll will be halved.

Burrowing: The curse lead to claws and/snout that are made for burrowing. You have a base burrowing speed of 20 feet and 5 feet in solid rock or walls. You can also build a permanent tunnel by burrowing at half your normal burrowing speed without the need of extra material. You have at least 5 feet of Tremorsense. If you already have Tremorsense it's range is increased by 5 feet.

Once you reach level 10, your are so used to and skilled with your mutated body that you are able to burrow at double your burrowing speed. You can also use your action to quickly burrow into the ground below you and prepare an ambush. You are able to conceal any indicaters of your recent digging when doing so. You can break your hole open at any point, spraying everything and everyone in a 15 feet radius with dirt or rock based on the location of your ambush and grapple who or whatever was directly above you.

The Hunger: The curse creates a monster of any form that is slave to it's hunger. You can consume corpses with no ill effects and heal 1 HP for every 5 lbs eaten. Some creatures can be frightened by doing so. You can eat up to 20 lbs of flesh each turn. You can also once per turn vomit a projectile with a range of 120 feet, dealing 1d10 damage, causing 2 HP of damage to yourself.

Once you reach level 10, your are so used to and skilled with your mutated body that you are able to consume the souls of creatures that you kill if they are at least 2 level below you. When consuming a soul you can cast a level 0 or level 1 spell that you know for free and no extra timecost.

Your mortal body is not equipped to host whatever evil hast invested your body. Every now and then, twice a day but never less than 2 hours next to each other, you have to rid your body of fluid buildup. Your body shakes and you go into shock as you vomit small amounts of acid for around 5 minutes. This acid can damage steel, wood and flesh, dealing 1d4 to 4d4 of acid damage based on how much contact was made. This can damage you or your items (weapon or armor) if you are unprepared or occupied and also everyone within 2 feet of you, friendly or otherwise. This breaks concentration, happens in both forms and can also happen in the middle of combat, costing you 2 turns.

These buildups happen at random and there are no saving throws against it. Tell your DM about this trait to be informed when it happens.

The curse has left you weak. You are half as strong against Diseases as most, you need 2 more days to fully recover and spending time around you for long periods of time has a chance to lead to diseases for others. While sick for any reason your movement speed is also lowerd by 10 feet. If your movementspeed falls below 1 feet, you are unable to move until you recover. This can stack if you are effected by more than one Disease.