Hermit Crab Grotto or just known as grotto is a neatly located dungeon at the end of hokurikudo 4th line. You can walk there from echigo and use "return to resurrection point" to get there faster (yeah there's a guide for that here).
My first try out is at lvl 82, when I'm getting my +100 sword w/2 ougis (main wep), I decide to go there with a support/wand hybrid, a support, and few passengers.. FYI I've been doing 2-4 man since lvl 70s to try how to wipe the mobs there but it seems kinda "complicated" in some ways so I have to stop.
the set I'm using is just regular.. 4 amara, 2 with good ornaments 2 with yes ornaments, no chian, no pop-star
2 wpn with ougis 1 updated, 1 older weapon and 1 old friend hitter.. and some good support. The first thing crossed my mind is.. Thunderbeast the entire room, well yes.. that's the fastest way to wipe out those damned blue penanggalan. At first room I've been zapping 2 times and.. guess what? dead. yeah, dead. why? because I start from the farthest middle and zap to the farthest mob from entrance, result is: 1. I escaped the ice balloon, 2. they don't cast anything, 3. dead.
I've been seeing a sword carry there, but didn't really saw him do what I did so I kinda rethink.. something must've gone wrong. Until I figured out: never, never cut your way between 2 sides of those penanggalan, ever.. they will cast the ice and it even hits you after you cast thunderbeast.. (dunno if it's even lingering hitboxes or what) from what I reserve from their ominous behavior, safest way to approach is make your way circling a group of penanggalan at close/mid range after that, zap them with thunderbeast! if your weapon or skill can't wipe them out in 1 zap, don't worry.. pan your camera 180 degree after you zap, then chain it with fast crimson flame/true spirit blast, or just regular skills like DSB, lightning slash/ phoenix slash, they all should be dead if you hit it right.
the 2nd room, it's kinda easy if you stay on the right track (my support even not giving me speed, to test out) I just do the usual routine: circle a pack, fast-compress it, thunderbeast > 180 > crimson flame > side roll, circle the remaining pack, thunderbeast > true spirit blast > clear the remaining if there are some.
I'm not giving all the details about the rest of the rooms.. but few notes:
1. don't get too close with kusareppou, centipedes, and those gankubi.
2. don't get too far and don't run straight against blue penanggalan they are better be approach when start moving in pack (don't wait too long either), and don't cast a thunderbeast from distance to a non-aggroed cause they will randomly strike you with balloons. And if you are confident about your thunderbeast wipe out, do 3-4 times with fast roll cancel. Note that you should make your thunderbeast angle as close as possible to a well-compressed pack, never stray out of pack or cut between 2/more packs, make a pattern that resembles letter of V, N, O, half O or Z with your thunderbeast or even M, tho M is kinda dangerous cause it cuts thru 2 packs.
3. The lag rooms. Take extra caution and planned strategies to clear these rooms, I believe the last room to be the most laggiest room ever of all the entire dungeons. There is small room packed with all sorts of nasty, evil looking mobs.. The idea is: 1. you rush through all of them with nasty zeal, and ends up standing frozen and even death. or 2. patiently took them off little by little and makes you safe. I never end up alive when I choose option 1, simply cause of lag. but then I rethink over another possible methods.. that is, BAIT. don't hesitate to use someone to contribute by being a bait, direct them to attract some of the mobs to the nearest corner and guard. Your job is now to wipe out these mobs, fast, and make sure you use your stronger skills 1st cause they will be aggroed to you, which is laggy. If you feel safe enough then you can wipe the rest of the mobs without baiting, but take extra caution of little freaking ants, it's lag inducing and super annoying if not wiped out fast.
4. The boss. The bosses are super easy if you ask me.. and it can be wiped by all other classes too.. they're not that high HP or defense so my 1x thunder should wipe them out easily, take extra caution for the Nue, their charge attack hurts.
exp earned is very rewarding, even more rewarding if you stay sharp and safe.. It gives 190k-200k per run at SS rank (I'm using premium tho) and 340k-ish using just 100% exp boost and login boost.. at lvl 83, which is jetplane exp. the chest at the end of the dungeon contains stones too, dunno if steal attacks bring out some rare drops. my fastest clear time is 11:04 mins and aiming for much faster but safer clear..
people at lvl 70+ you can encourage yourself to carry /proper 5 man there, even if you started with alot of dying, never give up!
and if there's grotto expert you can share your tips to me and some advice I'd use and giving feedback to each other~
UPDATE: those was my impression of early carry time there, the only thing need to be noted is you must mob them well. The details I can't spoken of as this kind of experience can only felt if you are actually carrying.. The blue penanggalans are not more than a fast-spewing, mid-shooting machine. They are actually avoidable even without speed, by making much narrower but perfect circle.
gankubi and kusareppou can easily mobbed. As for centipedes, they will stray and charge if you get too far from them so, mob them like C shape (start at right/left idm, gather them all like crescent).
for little ants, use fast aoe to dispose large number and make sure you don't running cause they will chase you, it is better to stay still and cast aoe (dodge if they start the bite animation, it kinda hurts).
intensive grind makes you better.. however focus is always a must
