I’ll give you the answer right off the bat: The date has been pushed but it seems like its happening still.
Back in 2021, it was announced that the valley would be home to the first Mattel Adventure Park, “an entertainment destination that brings together iconic Mattel franchises, immersing guests in rides and attractions designed to thrill, excite, and create epic memories.” Mattel is the company that produces all sorts of merchandise for lines such as Barbie, Hot Wheels, and Masters of the Universe/He-Man to name a few. Glendale was picked as the home for the Mattel Adventure Park which would be a part of a larger destination originally called Crystal Lagoons Island Resort that was set to open in 2021 but this eventually rebranded into a destination called VAI Resort.
The park is to have roller coasters such as “Hot Wheels™ Bone Shaker™: The Ultimate Ride” and interactive areas like the “Barbie™ Beach House™” which had the 2021 date moved to the new open by date of Q1 of 2023, then it became the end of 2024 and now its slated for late 2025. The reason for the latest delay is that VAI Resort is doing a phased opening, rolling out parts of the entertainment district piece by piece which includes Mattel Adventure Park. The VAI Resort website gives all the vibes of a typical Las Vegas casino destination with the Mattel Adventure Park tacked on as a bit of an afterthought. From it’s website, the opening statement from VAI Resort gives almost zero indication of what is sure to be the main attraction of the area (because how many entertainment districts does the valley need? Tempe Marketplace, Desert Ridge, Scottsdale, Westgate, etc, etc)

We do know that VAI has gotten past the hurdle of the city council vote so it SEEMS like its full steam ahead but we will keep waiting to see what this long awaited project has in store for the city of Glendale and the state of Arizona.