Gungho posted officially that there will be two new ultimate evolutions for Saiga and Apollo, the previous rare encounter and boss from the Choco collab dungeon (not sure if they will still be in the new one). You can see the details and evo materials below, as well as the materials to reverse evolution should you so desire. They are making it clear in their image that you can’t go in between one ultimate evo and another, basically you have to choose.
The new Apollo is fire and water element, keeps the same active skill and looks to have a leader skill of fire and water attack x2. For Saiga the ultimate evolution makes him dual light element and his new leader skill gives light element and god type attack x2. See the official images and details below, or you can click here for Gungho’s official page.