Luke Cage has met his match in Season 2. Bushmaster's (Mustafa Shakir) strength easily rivals his own, even though the new character's power comes partially from the Earth rather than a science experiment. What is nightshade on Luke Cage? Put on your best Severus Snape voice and turn to page 394, because Tilda (Gabrielle Dennis) is kind of a potions master — especially when it comes to this particular herb. Spoilers for Luke Cage Season 2 ahead.
In Episode 8, Bushmaster reveals that he's using a plant called "nightshade" to charge up his abilities. Later, the audience learns that he was given an experimental vaccine in Jamaica that killed everyone it was administered to except for him. After that, he started to notice that he was stronger, and special. Once you add nightshade, his strength becomes supernatural. So the plant doesn't give him his powers, it reveals whatever the vaccine did to him years ago. This isn't a super serum like Captain America or the heart-shaped herb in Black Panther. It's something in between. In Marvel comics, Bushmaster's powers are purely the result of an experimental treatment, more like Luke himself.
Mariah Stokes' (Alfre Woodard) estranged daughter Tilda, who is familiar with the plant, notes that it is poisonous unless used in small doses. Even before she met Bushmaster and started helping him, she carried nightshade and knew how to use it as a healing property.
In real life, nightshade is a genus of plant that includes some poisonous flowers, yes, but also common veggies like tomatoes, potatoes, eggplants, and bell peppers. Some people have nightshade sensitivities and should avoid those foods. There is also a plant called belladonna or "deadly nightshade" that is highly poisonous but used in stimulants, sedatives, and as a muscle relaxer. Though not named, that's likely what Shakespeare was going for in Romeo And Juliet when the young heroine used an herbal potion to appear dead and possibly also the basis for the Nightlock berries in The Hunger Games.
In Marvel comics, "Nightshade" has another meaning that's all too related to Luke Cage Season 2. Nightshade is the alter-ego of Tilda Johnson, a villainous scientist born and raised in Harlem, New York. Curious! In the comics, Tilda works with chemicals to enhance herself or others, and often feigns innocence to get in with those she plans to use or betray. One time, in the comics, Nightshade turned Captain America into a werewolf. She's one of the smartest people in the Marvel universe, and did team up with Misty Knight on at least one occasion, so she's not entirely evil.
Will Tilda follow down this path, and adopt "Nightshade" as her vigilante nickname? Towards the end of Season 2 she equips Bushmaster with enough nightshade to send him into a rage so he can kill her own mother. She definitely has the anger to become an antagonist, though loyalties are shifting left and right on Luke Cage. Is Luke helping Bushmaster take down Mariah, or helping Mariah take down Bushmaster? Who actually has Harlem's best interests in mind, and what exactly is Shades' endgame? Tilda may take the law in her own hands, but the shades of grey run deep on Luke Cage.
All in all, it isn't the nightshade itself that poses the biggest mystery on Luke Cage. Despite the fact that it sounds like something out of Harry Potter — and actually, it is something out of Harry Potter — the plant also exists in our world. It's what the Marvel characters do with nightshade that matters. This isn't the type of magic that MCU fans have seen in Doctor Strange, on Agents of S.H.I.E.L.D., in Wakanda or Asgard, or even with Iron Fist. It's natural, and the fact that Tilda and Bushmaster are bringing this to the Marvel Cinematic Universe is cool to see, even if their motives are murky at best and nefarious at worst.