Shapechange - Major

The character can take 1 minute to change into any known form and size, from an ant to a dragon. The character must know the form in order to take it, they can stay in this form as long as they like because this is actual shapechanging and not just assuming a form as it is not a spell like ability and can't be countered or dispelled via magic. a wish spell could wish them reverted or spells that force shapechangers into their normal forms work as well, but it takes a full minute to change so doing it in combat.. not the wisest of choices. 

The character must make a wisdom check ((DC 14)) or they remain stuck in that form for 1d12 days.

The character must do one of the following in order to learn new forms.

• Study the creature for 4-12 hours, learning its movement, habits, and behavior, the character must be able to be close enough to discern details (Higher CR creatures would take longer to learn then lower CR creatures).
• The character can spend an amount of time determined by the DM dissecting the creature, learning it inside and out.
• The character can devour the creature.
• The DM allows the character to know a creatures form for whatever reason the DM decides.

The character can choose to either have their equipment absorbed into them, or leave it behind in the change,  while equipment is a part of them, they gain no benefits from it.

The character gains/retains the following, in bullet format for easier reading.

• Retain their own Hit Points - They do not revert to their original forms when they die (Unless DM says they do).
• Retain their own Intelligence and Wisdom (Unless DM wants them to use the creatures stats fully). They retain their own personality (even if DM wants them to use full stat block of the creature).
• Can't speak unless the form they change to can speak at least one language.
• Can't change into Undead or Constructs.
• Gain any special skills of the creature but do not gain any spell like abilities of a creature.
• Gain any vulnerabilities, resistances, immunities, weakness's etc. that the creature has.
• Don't gain any legendary actions or legendary resistances the creature normally has.
• Other then Intelligence and Wisdom the character gains all stats of the creature, speed, skills, ability scores,  and senses the creature has.
• The character must know the creature well to be able to change into it, unlike wild-shape or polymorph, the character has to know more in depth details about the creature which can be obtained by one of the previous stated methods.
• If their wisdom or intelligence is higher or lower then the creature's normal stats, then skills based on those attributes need to be adjusted by appropriate amount.
• If the character is proficient in Wisdom or Intelligence saving throws and the creature is not normally proficient in them, the creature gains proficiency in them.
• Most characters will not know creatures with a CR equal or higher to them as usually they won't encounter things that strong until they level a bit unless GM allows that creature to be known by the character for backstory or whatever reason, but even if they know the form, they may not be able to assume it till they are appropriate level.
• To better balance this feat, the character can only assume forms with a CR 1/3rd their level or less, once they reach level 10 they can assume forms up to half their level in CR (level 10 would be 5 CR for example), once they reach level 20, all CR limitations are lifted unless the GM keeps them. 
• The character can't take any form with a fly speed until level 8, unless their default/true race has a fly speed already.
• The character can't take any form that has a swim speed until level 6, unless their default/true race has a swim speed already.