I noticed on Steam there is a "Not a Metroidvania" bundle, and it just strikes me as weird. Not necessarily wrong or bad, but I just can't think of another time I've seen a large game storefront actually use the term Metroidvania. Roguelike gets used a lot, but I'm pretty sure Rogue is open source and/or the companies that owned the rights have long since stopped caring because Rogue itself is not really a valuable IP at this point. Anyway:
I'm not a lawyer, and have no idea what the bounds of trademarks are. The Castlevania connection is tenuous, but "Metroidvania" does entirely contain the made up word "Metroid" that Nintendo owns the trademark for. I know you can't just call your game "Metroid", but I'm curious how far you can actually go. Can your advertising use the term "Metroidvania" and favourably compare a game to Metroid as much as it wants, so long as the game's title doesn't actually contain "Metroid" or obviously rip off Metroid art? I'm genuinely curious where the line is on using other people's trademarks.