I've been on several oasis class ships for hallloween before covid. There was always some sort of parade etc on the promenande. I'm with a group of 280 singles who plan on being in costume. I'm sure there will be something going on. I one ship I do remember a parade in the afternoon.
In Cozumel, I'm doing a day of the dead celebration - https://cozumelmycozumel.com/day-of-the-dead/?fbclid=IwAR0m5zFSYmnOaPYgXR5yM0YiE9Qt75wygtHhR0jdKJKCIMnyPNMxrZhl6Iw