Super Hero Taisen GP: Kamen Rider Sangou

Super Hero Great War Grand Prix: Kamen Rider 3 スーパーヒーロー大戦GP 仮面ライダー3号

Theatrical release March 21, 2015 (2015-03-21)

Kaijin

Spider type

The release date is like a countdown: 3-2-1.
It opens on February 10, 1973 (1973-02-10), which was the day the finale of the original Kamen Rider series aired.
Near the start of the alternate timeline, there's a Shocker GP to select new Shocker Jugend. This is a reference to Hitler-Jugend which means "Hitler Youth".
When Sangou saves Go and Yuuto from Garren, he bursts through the wall. In the first episode of Blade, Blade bursts through a wall to save Garren at the very beginning.
Zeronos says "let's meet someday in the future", which is a phrase his character utters in Den-O.
When Sangou is around, black feathers appear, foreshadowing his betrayal. When he turns good, the feathers are white.
When Minami Koutarou appears, he wears the same color scheme as when he appears on Decade. When he's Black, he wears fingerless gloves and a black outfit. When he comes back as Black RX, he wears a white outfit with a white jacket with black pockets.