Hilarious in Hindsight: A team named Gingaman shows up in episode 9 (turns out they're really villains), 8 seasons before Gingaman was a name of a real team of Super Sentai.
Moral Event Horizon: One episode has Doldora using her Monster of the Week to create an illusion of the Fivemen's mother in order to set a trap. Seeing the way Remi holds onto the hope that her mother might be real is enough to send Doldora over.
Billion gets a sword that makes its user Brainwashed and Crazy, as well as giving them evil powers. He gets one of Gaku's kendo students to use it, preying on the fact that the kid wants to be stronger in order to protect his parents because he knows the Fivemen won't kill the kid.
Then we have Garoa, after destroying the Fivemen's Humongous Mecha, but not the Fivemen themselves, he decides to draw them out, by attacking their school full of children. The scene with the children running to escape like they're about to die cements it. Shortly before these happens, he has dropped his Butt-Monkey status, if you didn't notice.
The true villain of the season, Vulgyre, killed Meadow when she refused his offer to rule with him, then impersonated her for the entirety of the season while destroying planets just to become all-powerful.