Actor Allusion: In the Hyper Battle DVD, the donut shop manager's big wish is to helm a dance crew. He's played by Kaba-chan, who's actually handled dance choreography before, such as the dance used in the music video for "Forest of Rocks", Movie Wars Ultimatum's theme song.
Yamamoto from #46-47 was previously Todoroki, whose actual surname was TodayamaAnd his Mage form is accented with green just like Todoroki!
Net Movie #24 has Koyomi dress up as a flight attendant. Her actor, Okunaka Makoto, is part of a idol group called PASSPO☆, whose theme is that of flight attendants.
There's also a supposed porn DVD cover with Hachi-Onna on it. It's not the same actress, but Hachi-Onna was once played by Nao Oikawa, who really used to be in porn.
In Wizard in Magic Land, the captain of the guard's Mage costume has a red cape; this isn't the first time Ryuji Sainei has played a leader in red...
Development Gag: Amadam describes the Riders' Phlebotinum Rebel nature using the term "Cross of Fire". "Cross Fire" was the original name of the concept that would become Kamen Rider.
Executive Meddling: On Twitter, writer Sho Aikawa explained that Masahiro Inoue's cameo in the post-script episodes was this, after a fashion. The staff wanted to bring back at least one veteran Rider as part of the Heisei-era celebration, but the producer said it would be pointless unless they could get "the first" (Joe Odagiri, the original Kuuga) or "the last" (Sota Fukushi, Fourze); then, almost as an afterthought, he added "Or it could be Decade".
I Knew It!: Due to a formula beginning to form with the previous Kamen Riders, many people began to guess at some tried and true theories and got this trope in return.
White Wizard being Wiseman? Many so called it.
Koyomi being the Macguffin Girl that everyone's after? A lot of people called it. Her dying prior to the finale? Most people called it. Her being revived? ...Actually jossed, to their surprise.