I remember playing a game when I was younger called "Guess Who". In this game, you have twenty-something pictures of different people, all with distinct features. One person picks a person among these, and the other has to ask yes or no questions about that person (ex. "Is he wearing a hat?") until they can guess who it is.
In order to make this into a more descriptive writing-focused activity, I think you could divide the class into pairs, and give each pair a couple pictures of people with very distinct features. Then, have the students each choose one person among these pictures, and write a paragraph describing that person in detail. This could also be a good time to have them implement any grammatical structures or new vocabulary terms you want them to focus on. After the students have written their paragraphs, have them exchange with their partners and guess who their partner wrote about.
This could also be turned into a whole class activity, like putting pictures of people up on the board or screen, having each student choose one to write about, and then share as a class. you could also have the students choose one of their classmates to write about, and everyone can guess who that person was.