Berry use triggers your custom status with the defined duration, the status ticks at intervals you defined. If you want an example, check SC_L_LIFEPOTION (Medium Life Potion, ID 12459) or any other similar status.

For stuff like that you're better off creating a custom SC_ status.

There's already bonus2 bHPRegenRate/bSPRegenRate which do exactly that. Check the documentation.

Remove that preserve change from the main block as well as the skill itself, and add it below that block, all by itself.

case ST_PRESERVE:
    if (sd && sd->sc.data[type])
        clif->skill_nodamage(src, bl, skill_id, skill_lv, status_change_end(bl, type, INVALID_TIMER));
    else
        clif->skill_nodamage(src, bl, skill_id, skill_lv, sc_start(src, bl, type, 100, skill_lv, skill->get_time(skill_id, skill_lv)));
    break;

Limit the skill's cast range in skill_db.conf and skillinfolist.lub (clientside), as it's 18 cells by default. As for your other questions, there isn't any noticeable impact as far as I know.

The message itself is missing from your msgstringtable.txt, actual line is 1863.

You can either update the file to include it or comment the line in pc.c evilpuncker mentioned to remove it entirely.

Sitting doesn't increase the amount recovered, it speeds up the ticks.

Go to line 12729 of status.c (going by stock Hercules) and change that bonus++; to bonus += (int)(0.5f);

This will reduce the tick by x1.5 instead of x2 but due to rounding up, the ticks will happen every 5 seconds and not 4.5, which is just 1 seconds faster than the default 6 sec interval when not sitting in case of HP recovery. The blocks above with RGN_SHP/RGN_SSP deal with regeneration that's boosted by passive skills (MG_SRECOVERY, SM_RECOVERY, etc) and would need to be modified in a similar way, which can be done by halving the val.

The skill protects from divests, it doesn't remove them.

Make it trigger a sc status that prevents sitting or create cansit_tick or something similar for the same purpose.

In the same way, you can add effects to any monster's ID, not all work properly though so you gotta test them.

Open monster_size_effect.lub inside the system folder, search for the DL's ID (1272) and delete the line including it ( [1272] = { MonsterSize = 1, MonsterEff = EFFECT.EF_DEVIL5 }, ).

This file adds special visual effects and changes the sprite's size for some monsters, like champions.

Chemical protection skills don't remove the divest statuses, they prevent them.

This would be more useful if it triggered when the player does damage, not when the player gets damaged, or maybe both options could be present.

Check the actual code for sling item, whatever you have pasted there is incomplete. Gut all the unneeded parts, modify what's needed, add defines for the items (itemdb_is_GNbomb/itemdb_is_GNthrowable by default), imitate that. Of course you will also have to modify the entry in skill_require_db to behave in a similar way or hardcode the whole new portion instead. If you want the skill to do both what it does normally and this new thing without interferences (like your issue with the caster getting item's status), you'll have to split it into two blocks, adding a check for having a throwable item equipped or something of the sort, could also make it based on skill's level.

This is something you'll have to figure out yourself, we don't know what's exactly going on there.

You need to create HP/SP values for levels above the normal maximum, check job_db.conf.

You need to create a new item script bonus, look at how ice pick's and similar bonuses are implemented to get an idea.

bonus2 bAddDamageClass,c,x;            +n% extra physical damage against monsters of class c
bonus2 bAddMagicDamageClass,c,x;        +n% extra magical damage against monsters of class c
bonus2 bAddDefClass,c,x;                +n% physical damage reduction against monsters of class c
bonus2 bAddMDefClass,c,x;            +n% magical damage reduction against monsters of class c

Check item_bonus.txt in the doc folder.

The file name is whatever you want to use that's inside the wav folder, just type it in. It isn't going to work all the time though. Often, the sounds won't play at all or do so randomly. It's pretty inconsistent and there aren't any better editors.

skill_unit_db (or skill_db if you're using a fresh version), declare a size for every level above 5 you want.

Most of them are declared in pc.c (pc_bonus stuff, for the list of constants go to enum status_point_types in map.h) and then obviously executed in the correspondent parts of skill/status/battle/clif/etc. Of course don't forget to flag them in const.txt

After a quick glance, this seems to just contain the outside NPCs in Lutie (instance creation, gear vendors and enchanters, etc), not the actual instance.

I'm personally sick of those jRO chibis being used in every single RO related thing nowadays.

Download the package.

Pretty sure that's a poorly translated script from this package:

http://herc.ws/board...es-package-v03/

Which is already working on hercules just fine (the entrance part and quests need to be sorted out though), so just look at the original.