Provided you have spent some time talking to a sentient creature (who speaks at least one language), you can make yourself look extremely attractive, according to their preference. You take on an illusory form that perfectly embodies that creature's ideal of beauty. As a result, you have advantage on Deception and Persuasion checks made when attempting to manipulate that creature, and you add double your proficiency modifier when making checks in those skills (if you're already proficient in Deception/Persuasion.) Other creatures can see the illusion as it appears to the NPC, but they are not affected by the enchantment. The spell lasts for one hour. If the caster is in the NPC's line of sight when the spell ends, the NPC becomes hostile to the caster, and any subsequent Charisma checks made to placate them are made with disadvantage.
The creature can, at any point, make an Insight check (if the DM decides that the NPC has become suspicious*) to gauge the caster's true intentions. The DC for the Insight Check is your spell save DC. On a success, your deception is immediately made known to them, and they become hostile towards you. Any subsequent Charisma checks made with regards to that creature are made with disadvantage.
*DM fiat on what makes the NPC suspicious. It can be a poor roll, or a player's faux-pas when role-playing the manipulation; E.g. the player (intentionally or otherwise) makes their true intentions known to the NPC while in-character. However, its important for the DM to take into account the potency of the illusion when making this decision.
* - (A pinch of gold dust)
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