The Mariners definitely leave an impression, but the two I've encountered so far in Limgrave and Liurnia aren't as dangerous as D made them sound -- the mobs they summon don't move fast enough to keep up with either the boat or Torrent, so I just kite them around a few obstacles (or the Mariner itself) and keep walloping the boss until all the dead things stay dead. (Presumably they're an even bigger joke if you've got access to holy attacks, but my Faith's basically nonexistent, so I just re-kill them the old-fashioned way.)

I think I was just overleveled for the one in the Limgrave! So it was more like smack it until it's dead (with occasional healing).

Probably. I bolted past in the first time on my way toward Caelid -- I was mostly just exploring and filling out the map, and heading for the border seemed like a good idea at the time (though I very swiftly realized it wasn't once I got to Caelid, and realized what some others had been talking about when they mentioned a 'hellscape'). It was only on my way back, somewhere around Level 55 or so, that I remembered the ferryman prowling the flooded ruins and stopped by to say 'hello'.

I think I was around level 20 or 22?..Not so sure, because I don't quite track this stuff and tend to go exploring when I cannot manage dealing with bosses. But Mariner looked silly, I was (yound and) unafraid, and had my Morgenstern +4 on me. Could've gone terribly wrong but it didn't.

I'm north of Level 60 now and still haven't cleared Stormveil yet -- I'm sure I can by now, but between the exploration and my favorite grinding spot that I stumbled across shortly after finding the Third Church of Marika, I keep finding excuses not to. I'm probably a bit neurotic about over-preparing for challenges.

Oh I feel you on over-preparing, though I am not quite on the same level. I check from time to time if I'm ready yet by coming to the bosses, looking at how quickly they kill me, and then either leaving or trying again. Castle Morne was a fine example of that! The first time I faced the boss in there, I was like "ugh, I can barely handle big harpies AND THIS IS EVEN BIGGER HARPY!".

Having the right stats and equipment for a fight can help, but for the bosses, it's largely a question of learned skill. The Demi-Human boss of Castle Morne is a good case in point: it moves fast and hits hard, but its attacks are easy to identify and there's a few windows to exploit when it misses -- dodging rather than blocking is a smart approach, for example, when the boss is swinging a massive sword with bestial ferocity like that.

Yeah, I realized that at some point. Though, I think, my win against it was a case of dumb luck: It pushed me into the corner of the fog gate, got locked itself by wolves, and on top of that I used grease, that quickens bleed accumulation. The smackdown felt really panicky but I was very relieved afterwards.

I think my next target would be the Runic Bear but man, bears are scary and I'm yet to defeat one.

When it comes to beast-type enemies, Bleed damage and fire tend to be your best friends. If you want to lean into making foes bleed out, try Fort Haight near the woods north of the Peninsula -- there's a recipe and materials for the Blood Grease, and the miniboss at the top of the fort drops the Bloody Slash art that inflicts massive Bleed buildup. (Also, if inflicting Bleed becomes a major part of your strategy, consider putting points into Arcane -- among its many effects is that it increases the rate of status buildup, like Bleed or Poison, on enemies.)

Been there, done that! :D For some reason was really fascinated to see roses there, hahah. Also thank you for the advice, I noticed that it affected luck (i think, i'm having a bit of a guess-game because of translation), but I didn't know about the status build-ups.

FromSoft could've done a better job of explaining what the different stats do, but it's generally easy to figure out. But yeah, Arcane is basically the game's Luck stat, and it affects everything from status rates (and, I think, critical damage) to item drop chance (and maybe rune drop as well, but I'd have to confirm).

The cataphract has become a splashaphract in his search for the one ring to rule them all.