While everyone in Hollywood transformed themselves into creepy characters for Halloween, Pia Mia spent the day at the beach!

The singer took to Instagram Monday to flaunt her bum in a sexy bikini, which appeared to be her costume of choice on the spooky day.

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The 20-year-old singer, who has worked with artists like Chris Brown and Tyga, is definitely a sight for sore eyes, and we've rounded up some of her sexiest Instagram photos in the gallery below!