xxdem

This is from my private source, you may consider yourself lucky...
 
https://pastebin.com/WhaKF4gV
 
to call it use the IJackpot interface, for example 
 
jackpotPick(allItems, L2DropItem::getChance);

probably they don't know what a proxy is, or that a loginserver should specify different gameservers from other locations (that are not connected by any mean ofcourse)

its the correct answer, you have to paralyze the character server side but without the frozen effect on the client side. In case speed is still an issue you should reduce the player's speed for that duration

Just add another level to hydro blast, lvl 29 lets say that has this unique description. Every skill level has individual description is skillname.dat
 
The server side is easier, you don't need the actual level server side, just send it through a packet to the player when he meets the conditions

There you go, I had the mood to create a sudo code for you, anyone with some knowledge should be able to implement it.
 
MultiSell, Time=12
RequestMultisellChoose, Item.setDestroyTimeStamp(System.currentTimeMillis() + MultiSell.getTime() * 3600000)
ItemExpireManager.registerItem(Item);
 
ItemExpireManager.registerItem()
{
     HashMap.put(Item, Item.getDestroyTimeStamp());
     Database.store(Item.getObjectId, item.getDestroyTimeStamp());
}
 
ItemExpireManager.checkForExpired()
{
     for each Item in HashMap
     if (timeStamp < System.currentTimeMillis())
     {      Item.destroy()
           Database.remove(Item);
     }
}
 
 
ItemExpireManager()
{
      for each Item by objectId in Database
      if (timeStamp < System.currentTimeMillis())
      {    Item.destroy()
           Database.remove(Item);
      }
      ThreadPoolManager start check routine every X seconds
 }

even if you get the "correct" values, your formulas are not the same with L2OFF formulas so you can't get even close