https://magic.wizards.com/en/news/mtg-arena/announcing-the-arena-powered-cube

The above article lists Pentad Prism as a card that can be obtained through Powered Cube Prize Packs or crafted with wildcards. It is however not a card that can be crafted. If the list is inaccurate it needs to be updated. If the list is accurate then the only people that have access to the card would be people who are buying in to the event and this may cause issues for any tournaments that happen.