Make the pineapple-infused gin: Trim the ends of the pineapple (reserve a pineapple leaf for garnish). Cut off the skin, then cut the fruit into 1-inch cubes. Transfer to a 1-quart jar and add the gin. Refrigerate at least 1 day and up to 5 days. Strain through a fine-mesh sieve.
Make the celery syrup: Bring 3/4 cup water, the sugar and celery to a simmer in a small saucepan over medium heat. Cook until the celery is slightly softened, about 5 minutes. Let cool, then strain through a fine-mesh sieve.
For each cocktail: Combine 2 ounces pineapple-infused gin, 3/4 ounce celery syrup, the citrus-vanilla liqueur, lemon juice, yogurt and bitters in a shaker with ice; shake for 30 seconds. Strain into a coupe glass. Garnish with a pineapple leaf.