Tensou Sentai Goseiger/Fridge

Brainwashed and Crazy Gosei Knight is specifically referred to as Dark Gosei Knight. Think that excludes him from the villains' movie Theme Naming? Think again.
Additionally, every one of Buredoran's faces was silver around the mouth, just like the Goseigers' helmets.
Buredoran's third form is called Buredo-RUN. The Matrintis are machine based, and RUN was the code used in the BASIC computer language to run applications.
Why do mecha get introduced in relatively quick succession within the Warstar arc? Because it's structured like a miniature version of Sentai arcs, complete with a Super Daibouken-esque mecha in the form of Hyper Gosei Great.
The cameo for the Goseigers and Double is very fitting...if you link the two anniversaries, Kamen Rider OOO and Kaizoku Sentai Gokaiger, this leaves Goseiger and W as Rider-Sentai counterparts.

Preemptively addressed with Gosei Knight - obviously he can't be shown pressing the Leon Cellular when he's in Headder form, so we see it floating in Hammerspace with the buttons responding to his thoughts.