Before we get in a revert war here. Casual formats can have banlists and wizards does not always maintains or even lists the banlist. Prismatic is not listed as a format on the official Wizards page at all, so citing the side claiming you find no banlist there is a bit dishonest. Example: Freeform is listed on the MTG page and does not have a banlist. So questions about this format can be easily verified via the Magic homepage. Prismatic has no entry at all. With this logic there are not even deck construction rules for this format in effect. In other word the official Wizards page is only so useful.
I don't have much experience with Prismatic or with MTGO but there are several sites giving a banlist for Prismatic like this for example: http://www.mtgoacademy.com/deckbuilding-rules-and-banned-restricted-lists/#9 I would assume that you can either look up the banlist directly in the MTGO client or due to an API or simply by being unable to add certain cards to the deck while constructing (this is a wild guess I have no clue how MTGO functions). - Yandere Sliver 05:57, 6 June 2016 (UTC)