Supergirl season one had an impressive list of villains in the first season, most of whom were borrowed from her cousins list of rogues. Toyman, Silver Banshee, Livewire and Reactron to name a few. And then there were others who we don't see as villains in the comics anymore after their rough start like Red Tornado and Indigo. Plus there were the alien group that included Vartox, Astra, Non, Master Jailer, Jemm and Hellgamite. And of course their version of Bizzaro.
The video below highlights the villains of the season, though they don't include Maxwell Lord.