There is a Halloween page on the DLP website, but it doesn't even specify yet when the season will start exactly or if there will be a party / parties. I think their main reason last year to do 2 parties is because of Oct 31st being during the week, and in 2018 the one party was quite busy. Tickets were on sale from mid April.
I've checked the Facebook event page for last year's parties, regarding tickets they made posts about buying your tickets (So by then they weren't sold out yet).
- Jul 26, Aug 30, Sep, 2 & 30, Oct 7,
- Oct 29th, still tickets available for the 31st (which was a Thursday)
As this year the 31st is on a Saturday, and with no doubt cost reduction, my assumption is there will be only be one party. If there is a party.
Just keep an eye on the
Disneyland Paris Facebook page, I would say.