Elden Ring Nightreign's map will sometimes see "large-scale changes" to terrain including procedurally appearing volcanos, forests, and yes, swamps

Elden Ring Nightreign screenshot which highlights just how important co-op will be because of towering spider threats.

Elden Ring Nightreign isn't messing with a good thing, so you can expect some gnarly swamps to ruin your day and honor FromSoftware tradition. Lovely stuff.

Speaking to PC Gamer in magazine issue 405, director Junya Ishizaki shares that the map sometimes sees "large-scale changes to terrain in the form of procedurally appearing volcanos or swamps or forests."