Syonide debuts in the Isabella, Von Eeden and Colletta tale from Black Lightning 6 (Jan 78), which fills in some of the hero's backstory.
Black Lightning finally figures out that Gambi has been kidnapped, and gets on the trail of the men behind it. He fights two goons, but gets taken down by a drugged dart fired by their boss, Syonide, who kidnapped Gambi in order to lure the hero to him. Tobias Whale has placed a huge contract out on Black Lightning, which Syonide intends to collect.
Two-Bits comes to the hero's aid, and Black Lightning explains to him how Gambi essentially raised him, along with his mother, after his father's death. Jefferson Pierce grew up in the tenement directly above Gambi's tailor shop. Now it feels like his own father has been kidnapped.
Back at the high school, there is yet another scene with Jefferson Pierce avoiding Lynn Stewart, but we finally learn the reason why when Lynn reveals that she and Pierce used to be married. So not only is Black Lightning the first black hero in DC Comics, he is also the first divorced one.
Black Lighting is so intent on finding Gambi that he walks right into Syonide's trap. His electric force field is able to neutralize Syonide's charged whip, but by torturing Gambi Syonide has learned how to nullify Black Lightning's force field as well.
Ultimately, that doesn't even matter. Syonide had drugged Black Lightning the night before with a toxin that knocked the hero out immediately, but which also had a delayed effect, and now leaves him unable to move on his own. Syonide puts a rope on him to bring him to the 100 and collect his bounty, but also reveals that Gambi was the man who killed Black Lightning's father.