[GrandComplete]

I'm not sure this counts but Kamata from Decade. He was both Kamen Rider Abyss and the Paradoxia Undead. And overall he's just a great villian for Decade. From the fact that he was from Blade world but was also the main villian of Ryuki was a great way to pull of Decade world fusion conflict.

Plus both of his forms were also great within the context Decade. Since with the Rider decks in Ryuki were all originally blanks that had to be filled with a contract so seeing in Decade anew Ryuki Rider whoose Contract Monster which was just a regular MOTW in Ryuki is a great blend of Ryuki and Decade.

Then the Paradoxia Undead was one of the couple that was never unsealed in Blade. So it's great to finally see one of them. Once again playing up Decade A.R concept