I am going to try and connect some weird pieces here.
Whipacorn from The Dreamers deck mentions Mainstay in its flavor text. Ra asks why a unicorn would have a whip for a horn, and Mainstay says "For Whipping!" This joke has more context to it.
Iron Legacy's Iron-Fist Strike card shows him kindney punching a rather large biker dude complete with mom tattoo and chains. What does that dude have chains for? Well, I think maybe for whipping.
The definition of mainstay from the Merriam-Webster dictionary
1: a ship's stay extending from the maintop forward usually to the foot of the foremast
2: a cheif support
In ships with more than 3 masts (the tallest one being the main mast), the biggest strongest cable that is attached to the main mast is called the mainstay. We do have a villain with a pirate ship. The plot thickens!
La Capitan's nemisis icon has some weird stuff going on, but if theres one thing I can say for certain about it, it's that there is a chain in that icon. What does that icon have chains for? Whipping! I think I like where this is going.
Some other quick thoughts about this dude.
The mainstay on a ship runs forward from the main mast (the one runing behind is the backstay go figure). If our Mainstay turns out to be a nemisis of La Capitans, I do not think it would be a stretch to think that he was a part of the crew at one point. Runing away from the old crew, being in front of them so to speak? Maybe he was even first mate given the context of his name.
Going back to Iron-Fist Strike for a moment, it does not seem like Mainstay is holding his chains does it? Possible he dropped them with the force of ILs punch, but the positioning would seem odd if that were the case. They are kind of going around his arms, almost as if it were restraining him to something. Look closer. It seems like there is something being shattered behind Mainstay. Metephor for IL breaking his will to fight back, or something more? My mind is picturing that he is always bound to some psycic mast for whatever happened between him and the rest of the La Capitans crew, though that is not based on anything.
Could I be on to something or am I like way off the mark here?