Even if you don’t watch OOO, for whatever reason, if you have ever watched a Kamen Rider I feel you need to watch episodes 27 and 28.
aka the time Kougami in honor of 1000 episodes
canonically made a Kamen Rider movie
with so many fucking references to the original Kamen Rider
and that one scene with Kougami where he had on all of the Kamen Rider Openings playing
including the Kamen Rider OOO opening