According to their events website, there are no activities planned for tomorrow night in Grande Case. See image below or follow the posted link.
St Martin - Carnaval agendaSo just rereading all the responses and it turns out that on Tuesday 21 Feb, there’s Harmony Nights at Grand Case
AND
Mardi Gras Carnival in Marigot. So now I’m debating, maybe Marigot might be a different, more local experience and true Mardi atmosphere?
Edit: the more I read, the less I’m certain.