1. The Fastest Man on Earth (S1) - Supergirl and The Flash join forces against Silver Banshee and a returning Livewire.
2. Amazonian, The (S2E02) - Supergirl teams up with Wonder Woman (Lauren Morano) against the Greek war God, Ares.
3. Starro the Conqueror (S1) - in the first season finale, Non and his boss, Starro The Conqueror (Ben Kingsley), alongside their army of White Martians threaten humanity, prompting Supergirl, Martian Manhunter, and Superman (Henry Calvin) to subdue the threat for good.
4. The Return (S2E01) - in the future 2nd season opener, Supergirl still working with the DOD encounters a returning Bizzaro-Supergirl who is framed for the murder of Maxwell Lorde, which she did not commit. They join forces to clear Supergirl's backwards yet monstrous foe turned friend's name.
5. War of the Worlds (S2E03) - Supergirl defends National City from an alien brute known as Mongol from the planet War World.