Superman & Lois: What is X-Kryptonite?

In the pre-Crisis on Infinite Earths continuity in the comics, Supergirl and Superman would run into a lot of different strains of Kryptonite, each with its own unique effect on those around it — usually, but not always, Kryptonians. Whether it was blue Kryptonite, which would temporarily strip Kryptonians of their powers, or gold Kryptonite, which would do the same, but permanently, or red Kryptonite — which had a wide variety of unpredictable effects, but the most commonly used one was turning the person evil temporarily — well, the point is, there were a lot of different types of Kryptonite. So many that it’s hard for a casual fan to keep track of all of them.

One of the ones that didn’t get a ton of play was X-Kryptonite, which surprisingly made its live-action debut on Superman & Lois tonight. Kind of a Bizarro version of blue K, X-Kryptonite gave non-Kryptonian an approximation of Kryptonian powers temporarily.

Minor spoilers for Superman & Lois to follow.

The most notable example in the comics is Streaky, the Supercat, a stray cat taken in by Supergirl who later got powers accidentally due to exposure to X-Kryptonite. In the comics, it was created as a result of a laboratory experiment in which Supergirl was trying to render green Kryptonite (which is toxic to Kryptonians) inert. In a wildly irresponsible moment, she became frustrated with her lack of progress and threw the X-Kryptonite out the window.

(Since the experiment had failed, she thought she was throwing green K, which is toxic to her and to Superman, out the window. Why would she do that?!)

Streaky happened upon the X-Kryptonite and got her powers, becoming a sidekick of sorts to Supergirl until a later accident which transformed all Kryptonite into iron. Without proximity to X-Kryptonite, Streaky lost her powers.

In Superman & Lois, tonight’s episode (“Haywire”) ended with Morgan Edge and Leslie Larr — the woman we saw unleasing heat vision last episode — found a cache of X-Kryptonite — presumably a naturally-occurring variant, or one that was chemically changed by its interaction with coal, since it’s in a mine, as we are to assume it was in a previous community. The plan, apparently, is to build an army, but that raises the question: what would happen if the X-Kryptonite were to be destroyed or rendered inert?

Superman & Lois airs on Tuesday nights at 9 p.m. ET/PT, following episodes of The Flash on The CW.