True Polymorph

9th-level Transmutation
Casting Time: 1 action
Range: 60 feet
Components: VSM (a drop of mercury, a dollop of gum arabic, and a wisp of smoke)
Duration: (C) 1 hour

Choose one creature or nonmagical object that you can see within range. The creature shape-shifts into a different creature or a nonmagical object, or the object shape-shifts into a creature (the object must be neither worn nor carried). The transformation lasts for the duration or until the target dies or is destroyed, but if you maintain Concentration on this spell for the full duration, the spell lasts until dispelled, or until you use your action to end it.

A shapechanger can automatically succeed on any saving throws against this spell, and it has no effect on a creature with 0 hit points or a corpse. An unwilling creature can make a Wisdom saving throw, and if it succeeds, it isn't affected by this spell.

Creature into Creature. If you turn a creature into another kind of creature, the new form can be any kind you choose that has a Challenge Rating equal to or less than the target's Challenge Rating or level, but no higher than 20. The creature transforms into an average example of the chosen creature. The target's game statistics, including mental ability scores, are replaced by the statistics of the new form, though it does not gain any Spellcasting, Innate Spellcasting, Legendary Actions, Legendary Resistance, Mythic Actions, Villain Actions, or Lair Actions the creature may have. It retains its alignment, personality, and any languages known.

The target assumes the hit points of its new form, and when it reverts to its normal form, the creature returns to the number of hit points it had before it transformed. If it reverts as a result of dropping to 0 hit points, any excess damage carries over to its normal form. As long as the excess damage doesn't reduce the creature's normal form to 0 hit points, it isn't knocked unconscious.

The creature is limited in the actions it can perform by the nature of its new form, and it can't speak or take any other action that requires hands or speech unless its new form is capable of such actions.

The target's gear melds into the new form, and is replaced by any equipment used by the new stat block, which disappears when the spell ends. The creature can't activate, use, wield, or otherwise benefit from any of its original equipment.

Shapechange. When you cast this spell on yourself, you gain the effects as described above, but with the following changes:

The hit points of your new form becomes 350, regardless of its normal hit points.
For the duration of the spell, you can change your shape to another creature of your choice. When the spell becomes permanent, you remain in the shape of whatever creature you were when the spell ends.
You retain your Intelligence, Wisdom, and Charisma, unless your form has a higher score, though you retain your original spell save DC and spell attack modifier. You also retain all of your proficiencies, in addition to gaining the proficiencies and languages of the creature.
You retain the benefit of any features from your class, ancestry, or other source and can use them, provided that your new form is physically capable of doing so, including spellcasting and special senses. As long as the form has a mouth, it can speak, even the creature normally cannot communicate.
You choose whether your equipment falls to the ground, merges into the new form, or is worn by it. Worn equipment functions as normal. Your equipment doesn't change shape or size to match the new form (unless it is magical) and any equipment that the new form can't wear must either fall to the ground or merge into your new form. Equipment that merges has no effect in that state. If your new form has equipment in its stat block, you may choose to have it appear when you transform.

Object into Creature. You can turn an object into any kind of creature, as long as the creature's size is no larger than the object's size and the creature has a Challenge Rating of 9 or lower. The creature is Friendly to you and your allies. In combat, it takes its turns immediately after yours, and it obeys your commands.

If the spell lasts more than an hour, you no longer control the creature. It might remain Friendly to you, depending on how you have treated it.

Creature into Object. If you turn a creature into an object, it transforms along with whatever it is wearing and carrying into that form, as long as the object's size is no larger than the creature's size. The creature's statistics become those of the object, and the creature has no memory of time spent in this form after the spell ends and it returns to normal.

At Higher Levels. When you cast this spell using a spell slot of 10th level, the duration is concentration, up to 10 minutes. When you cast this spell using a spell slot of 11th level, the duration is concentration, up to 1 minute. When you cast this spell using a spell slot of 12th level, the duration is instantaneous. Additionally, the CR of an object turned into a creature increases by 1 for every slot level above 9th.

Source: PHB 283, SRD

Changelog

Altered range from 30 feet to 60 feet.
Added upcasting option.
Clarified restrictions on creatures that can be transformed into, equipment conjured by certain stat blocks, and parts of stat blocks that are not retained (Legendary Actions, Resistance, etc.) Additionally, added a CR upcast benefit to creature into object.
Updated parts of the spell (can't target corpses, don't get spellcasting, keep original languages) based on the new version of the spell. Folded Shapechange into a self-cast function of Creature into Creature. Now also a Druid spell.