The swamp is the first massive difficulty jump for sure. Meadows to black forest is perfectly fine and then you get to swamp and everything is death until you know exactly what to do.

Poison resist meads are a must, and if you do have mead production up already you can also make at least the minor healing and stamina meads to help you survive as well. I would recommend that the first time you get to a swamp, grab some turnip and gtfo for a bit. The turnips will let you make a spice rack to upgrade your cauldron with so you have some better food options as well. A hoe is also one of your best weapons for the swamp. It does no actual damage, but it can help you deal with the terrain being your biggest enemy, plus you can cut off different pools from each other so you dont get so incredibly overwhelmed by leeches either (still wouldnt recommend trying to land your ship in the swamps, leeches maul those to and the undead have no issue firing arrows from underwater where you might not be able to fire back). With the spawners you either have to rush in and wreck them before they can spawn enough to overwhelm you, or take potshots from afar with your bow until they finally go down. If its a geyser spawner, break out the hoe and level the ground to just under the water level. Water hurts the surtlings so you just turned that fire hazard into a passive core farm instead.