Saw this posted over at wdwmagic.com:
On select summer nights starting June 21 2018, special lighting effects will transform the water park like never before as Buzz, Woody and Jessie throw a Beach Party inspired by their friend, "Partysaurus" Rex. Come join the fun, dance on the beach, play party games, and meet up with Buzz, Woody and Jessie, plus, all attractions are open for guest enjoyment.
Disney H20 Glow Nights will take place only at Typhoon Lagoon on Thursdays and Saturdays from June 21-August 11, from 8-11pm.
Disney H20 Glow Nights are a separate ticketed event and the party is not included in daytime admission. Tickets will go sale March 19 and cost $55 for adults and $50 for children ages 3-9 (plus tax).