You curse and transform a humanoid that you can see within range that has at least 1 hit point into a new form. An unwilling target must make a Charisma saving throw to avoid the effect. A humanoid with the shapechanger tag affected by this spell (e.g. werewolf) can revert to their normal form as an action, ending the spell. A target whose challenge rating (or level if it doesn't have a challenge rating) is higher than the slot level used to cast this spell can repeat the saving throw at the end of each of its turns. On a successful save, the spell ends. If such a target fails three of these saves, the spell lasts for the duration. 

The new form can be any Medium or smaller beast that you have seen before whose challenge rating is 1 or less. The target retains its hit points, Intelligence, Wisdom, and Charisma scores, as well as its alignment and general personality. The target's other game statistics are replaced by the statistics of the chosen beast or the closest one that resembles it, except the target has disadvantage on attack rolls, ability checks, and saving throws for the first hour following the transformation. The target is considered to have both the beast type and humanoid type while transformed. As such, any game features that can affect beasts or humanoids can also affect the transformed target. 

The target's gear melds into the new form. The creature can't activate, use, wield, or otherwise benefit from any of its melded equipment. When a beast tries to wear or use any other item, DM adjudication is required to see if the item functions as intended. The creature is limited in the actions it can perform by the nature of its new form, and it can't speak or cast spells, unless it can do so without any verbal, somatic, or material components. It can, however, communicate telepathically (if it normally has this ability) or concentrate on a spell that it cast before being transformed. 

The target reverts to its normal form when the spell ends, or if the curse is removed. Only a greater restoration, a remove curse spell cast using a 5th level slot or higher, or a wish can lift this curse and end its effect. A dispel magic spell or a remove curse cast using a spell slot lower than 5 suppresses all effects of the curse for 1 minute-- after which time the target resumes its beast form. If a cursed target dies, it doesn't revert to its normal form. If it is raised from the dead while the curse is still in effect, the target retains its beast form upon revival. 

The cursed target can't be affected by another polymorph spell, unless the spell slot used to cast that spell is higher level than the one you used to curse him. If the effect of a polymorph spell ends on a target cursed by this spell, it reverts back to its cursed beast form. 

At higher levels. When you cast this spell using a spell slot of 6th-level or higher, the duration becomes 24 hours for a 6th-level slot, 7 days for a 7th-level slot, 30 days for a 8th-level slot, and permanent for a 9th-level slot.