For starters, a new Rider named Kamen Rider Necrom will appear. This Rider will have an eye drop motif and transforms using a brace-type transformation device called Megaulodor. That being said, instead of shouting "Kaigan" it shouts "Tengan" (trans. clairvoyant or eye drops).
In addition to that, Kamen Rider Ghost will get a new form, the Ghost Fighting Spirit Boost, which will use a sword called Sunglasses Rusher. Lastly, Kamen Rider Specter is said to transform into Houdini Damashii. Accordingly, some parts of his bike, the Machine Hoodie will combine with him to transform into Houdini Damashii.
[Source: The Ghouly News Tumblr (link 2)]