Ok, so I have seen a lot of people asking about Battlegrounds/God Items/Cash Shop/Event Items/Mobile Items/Custom Items, it usually becomes a major bore to repeat the same thing over and over again, so I have put their obtainability here:
Battleground:Mainly asked due to the number of people going OMGWTFBBQ at their PvPing value, if your server has them then it is either obtained by 1) Customized Quest, or 2) Your server has the battlegrounds, battleground items are technically untradable unless your server has some kind of customization, you can find a list of BG Items and their info here:
http://ro.doddlercon.com/wiki/index.php?title=New_Armors#Battlegrounds_Update_Equipmenthttp://ro.doddlercon.com/wiki/index.php?title=New_Weapons#BattlegroundsGod Items:Again, mainly asked due to their pretty high stats, they are made from a quest involving some hard castle drop treasures, for SE castle drops, the trial is even harder, sometimes servers have them as a simpler form of quest, they are also common for admins to put them as Donation Items, this is the list of god items:
Sleipnir
Megingard
Mjolnir
Bringsman
Bryhindr
Aesprika
Cash Shop Items:Cash shop items is something Gravity made to increase their income from RO, since most pservers use customized donations systems, they tend to be unobtainable, usually, you can obtain them from customized quest NPCs, most of these kinds of items comes in boxes or have the word "Rental" infront of them, so it's not THAT hard to guess where they come from, but there are still some hats without these prefixes
Event Items:These items were made for special official server events, no way of obtaining them outside of customized-related-crap, check above for how to obtein them
Mobile Items:Likewise, these items are obtainable by playing a mobile phone RO game, since pservers don't have any connectability with these soo... it still can be obtained if your server has any kind of customization like above
Custom Items:Each server has it's own difference ways of obtaining them, don't bother to ask it here