In the latest trailer for next week's episode of Supergirl, longtime Superman villain the Toyman is out of jail and staging a battle against the police...and Supergirl.
What's arguably the most interesting is a brief glimpse we get at the end of the trailer, of a Supergirl toy that marches toward the real Supergirl and, apparently, opens the "S" emblem on its chest to reveal something.
There's a few green lights that seem to move around the "S" before it happens, but when light starts emanating from the doll, it bathes the screen in red...
...what could it be?
Well, it doesn't seem too unbelievable to guess that Red Kryptonite might be making its way to the series.
What's Red Kryptonite? Well, it depends on who you ask.
In the pre-Crisis on Infinite Earths continuity, Red Kryptonite was just standard green Kryptonite, which had passed through a mysterious red cloud. It would affect Kryptonians in seemingly random ways, with no two chunks having the exact same effects or signature. After a period of 1-3 days, the effects of the Red K would wear off and that specific Kryptonian would be immune to that specific piece of Red K forevermore.
In the post-Crisis era, the first Red K was a lot simpler: It took away Superman's powers. That one wasn't actually radioactive, but had been created by Mr. Mxyzptlk.
Later, cosmic villain Dominus would create one that caused Superman's head to grow, and later still, Ra's al Ghul synthesized some that would make Superman's skin translucent, increasing his power consumption and making his powers go out of control -- which is similar to what they'd done on the Lois & Clark TV series. The Superboy and Smallville shows both gave us Red K that impacted young Clark emotionally in significant ways.