By secondary i mean we exclude characters who were main antagonists in arcs of DB/Z/GT/S, movies or games or were heavily responsible for existence of main threats (like Gero) and i obviously don't count any dumb FUNimation "arcs" like "Captain Ginyu saga".
so those characters are 100% not allowed:
I know the choice is pretty limited and most side antagonists weren't great but let's try and find some good as well.
I wasn't sure if i should put Hit and Rildo since despite being main fighting antagonists in arcs they were both only following orders of Champa and Myuu so i didn't put them on this list. Jiren was a bit different case. Also both are cool and overall liked characters so it'd be a waste if we excluded them.
Examples of characters allowed to help you choose:
-Raditz - underrated character considering he is brother of Goku. He had cool design and techniques and fight against him was one of the best fights in DBZ
-Android 18 - franchise lacks female antagonists or characters in general, especially relevant ones, and she was no joke completely trashing super saiyan
-Rildo - he had cool powers and his presence added tension that series didn't have since Namek
-Oceanus Shenron - DB lacked characters like her after first series. Funny and perverted character. Real threat despite being born from wishing a panties by Oolong.