As an action you may transform into one of your listed forms, lasting an amount of hours equal to your proficiency bonus or until you finish a rest. You must finish a short or long rest before you can transform again. Each transformation has some benefits and some detriments, as well as personality alterations. Additionally a transformation may be triggered involuntarily based on specific stimuli, with the same rules as when you transform willingly.
Beastly: Hunter or hunted
While transformed you gain advantage on two of the following skills of your choice (chosen when you transform): Acrobatics, Athletics, Perception, Survival or Stealth checks as well as Constitution saving throws to avoid exhaustion, ignoring the effects of the first two levels of exhaustion (you still need 6 to die), due to your heightened survival instincts and increased durability.
However you become more emotionally unstable and impulsive gaining disadvantage on all Wisdom saving throws, as well as Intelligence checks made to recall information. Also whenever you start your turn with half or less of your hit points you must make a DC 15 Wisdom saving throw or become frightened by the most severe threat that you can perceive until the start of your next turn.
Lastly, in addition to the personality traits mentioned above you also have the feeling that you are being stalked by something far stronger than you, and you must take precautions in order to not become prey.
Elemental: Serenity in apathy
While transformed you are in a constant state of calm, allowing you to focus more intensely. If you would fail a Concentration check you may as a reaction reroll one of the dice rolled, adding your proficiency bonus to the new total. Additionally you become far better at tasks that require your attention for more than 15 minutes. When making any check for such tasks you have advantage, adding half your proficiency bonus to the check if you aren’t already proficient in it (rounded down).
However you have a tendency to respond to danger of any kind with an apathetic attitude. You have disadvantage on Insight checks and attacks against you are made with advantage each turn until you are hit, this effect refreshes at the start of your turn. Also you aren’t fully attuned to your more fluidlike form yet, gaining disadvantage on Strength saving throws.
Lastly, in addition to the personality traits mentioned above you also have a great feeling of self righteousness, and you will calmly yet firmly defend your opinions and decisions.