Wada Arco teased the full appearance of Kingprotea Alter on her Twitter. She appeared in the story of Lostbelt 7, which went live in the Japanese version of Fate/Grand Order in late December 2022. Kingprotea will also be one of the Servants available to summon for the New Year’s, as well as being on the GSSR banner for the Extra Class. [Thanks, Famitsu!]
FGO第2部 第7章「ナウイ･ミクトラン 惑星を統べるもの」にてオルタ化したキングプロテアを描かせて頂きましたー！🌏😈
— ワダアルコ🌹 (@tsubuanfes) January 4, 2023
She will not be a separate Servant. Instead, this will be a costume dress for the existing Kingprotea Servant. As opposed to the more wild child-looking Kingprotea, Kingprotea Alter has a skintight suit on, with a large headdress. Underneath her headdress, we can see that she has a headband on. Her horns are not present.
You will be able to get the Costume Dress for Kingprotea Alter when the second half of Lostbelt 7 goes live in late January 2023. You will likely need to complete Lostbelt 7 first before you can unlock it. There are a few differences between the Costume Dress version and the one that appears in the story. But neither Lasengle nor Wada Arco have specifically pointed them out.
Fate/Grand Order is readily available on mobile devices, and the Kingprotea Alter Costume Dress for Kingprotea will go live in late January 2023. This skin will only be on the Japanese server for now.