This week's episode of Supergirl promised the return to the storyline of fan-favorite characters Lena Luthor and James Olsen (and their not-necessarily-fan-favorite budding relationship) after a string of episodes focused overwhelmingly on Kara and her fellow aliens taking on prospective world-ending threats, along with the return of Lena's corporate foe Morgan Edge. But the episode also featured a comeback that most didn't see coming (at least not at this juncture): Lillian Luthor, Lena's supervillain mother, who reinserted herself into a game of assassination cat-and-mouse between her daughter and Edge that also functioned as a none too subtle metaphor for Lena's inner battle with her own duality (she wants to be one of the good guys, but Luthors are just so good at being bad...)
The whole shebang came together in a mostly satisfying way, dovetailing with a B-story about Sam (aka Reign) admitting to suffering from unexplained blackouts (when she doesn't remember being Reign) to her friends and getting tested but mainly spinning off into a clever four-way game of motive and opportunity: Morgan Edge is trying to kill Lena, Lillian tries to kill Edge "for Lena" (and also to nudge her toward her own dark side), James suits up as Guardian (remember that?) to protect her and investigate/threaten Edge, Lena tries to thwart her mother and also finish things with Edge without necessarily killing him. Alex, Kara and the DEO are also involved - though more in a "support" capacity right up to the point where they can't be anymore.
Obviously, since this is Supergirl, there needs to be a mid-story cliffhanger for some tension (Lena gets poisoned, which is negated by use of Kara's freeze-breath which makes scientific sense because shut up) and eventually things need to get blown-off with a big super brawl - this one featuring a big DC fan treat in Lillian paying off that tease of Lex's strength-enhancing warsuit from the Silver Age comics (which Supergirl has opted to christen "The Lexosuit") from way back in mid-season 2. Even with all that going on, this is still ultimately a "breather" episode from the running main plot of Kara versus Reign, though, so we wrap with things mostly on hold. Lillian Luthor is off to jail, but she'll be back. That's another potential semi-regular bad guy for season 3's roster, not even counting the three other Worldkillers who've not officially joined the main story yet... is that too many?
Fans of superhero media spend a potentially inordinate amount of time on the question of how many villains is too many. Whereas at one point it might have been assumed that afficionados of the genre would enjoy seeing heroes taking on whole legions of familiar foes (once upon a time famously-unfilmed screenplays for projects as diverse as Dazzler or early drafts of Spider-Man often featured whole caches of costumed enemies), the box-office disappointment of Batman & Robin instilled a supposedly common nugget of wisdom in the minds of the viewing public that "too many villains" was a sure sign of a comic-based property about to make a serious misstep. Many would also point to the divisive Spider-Man 3, which featured three nemeses after the first two films had centered on one apiece, as further proof of the calculus.
Like many such cultural memes, there's a semblance of logic to the idea of "villain overload." Superheroes originated as static characters whose origin stories were pre-set and whose issue-to-issue adventures were defined by the challenges set up by their enemies, who were different every issue in order to give readers an easily visible confirmation that this new story was different from the one they may have bought and read previously. That tradition carried over into animated cartoons that brought superhero characters to a wider audience, and also to the Adam West version of Batman, which typically pitted the Caped Crusaders against a different foe from caper to caper (adaptations of Wonder Woman, The Incredible Hulk and Spider-Man typically featured more mundane enemies or figures made up for television, instead).
Modern superhero series and movies, on the other hand, have trended toward more serialized forms of storytelling and routinely feature multiple villains - though often organized into heirarchies. Batman Begins has at least four (a mobster, The Scarecrow and two incarnations of Ra's Al Ghul), Iron Man and Captain America tend to take on entire organizations (or each other) and on television one often finds "season arc" villains, interspersed with one-off foes dropped in along the way. That's the model Supergirl has thus far followed, though season 2 pulled something of a fast-fake by swapping out apparent main villainess Lillian Luthor with Mon-El's evil mom as the "real" big bad for the big finale. Season 3 is all about Kara versus Reign (and her mysterious handlers) with minor deviations along the way... or at least it was.
As of now, Supergirl season 3 can now count Reign, her master(s), The Worldkillers (unless one or more turn out to be "good"), the evil Rao-appropriating cult leader, Morgan Edge and now Lillian Luthor as significant main-story threats with the episode-order not even half completed - meaning it's likely that there are more to come if the first two seasons were any indication. That's an awful lot of bad guys for one series to juggle, and that's before one remembers that Supergirl is often primarily focused on dramatic storylines about character relationships that don't involve the villains primarily or even at all (though it feels fairly likely that the time-travel storyline that's caused the love-triangle between Kara, Mon-El and Imra will eventually prove to be tied to Reign etc before the season is out.)
On the other hand, Supergirl has deftly juggled multiple tones and story points before, so a plurality of villainy shouldn't necessarily be any more difficult to manuever around than the multitude of romantic pairings that dominated season 2's B-stories. Season 3's running theme has focused overwhelmingly on building up Kara's ability to withstand a breaking-point of personal and professional obligations piling up all at once, so the abundance of seemingly major threats is clearly part of an intentional extension of that theme. But intentions can still backfire, and fans will no doubt be on the lookout for whether or not Supergirl can grapple with this conundrum that's scuttled so many super-properties before it.