I have seen a lot of misinformation about Premium Characters on the web, so I decided to upload this pure facts video.
There are 3 free Premium Character slots (separate from normal character slots).
Premium Characters can join Red Battlefield, Arena and Arusha's Stadium.
Premium Characters don't have any access to Warehouse/Marketplace and can purchase only HP/MP(EP/FP/SP/DvP) potions + items shown in this video.
For whatever reason Premium Character creation closes(crashes) the game within few minutes on my end (game logs say that there is a Reconnect Fail, and it gracefully shuts down the client, but it's not like I get a DC or something, maybe it's a server-side thing), so I created my Premium Witch with default appearance and named her Crashes. She lived up to her name and made me crash with BSOD from Red Battlefield. My system is rather stable and I haven't seen any BSODs for years! I haven't experienced any problems with my normal characters, so this has definitely something to do with Premium Characters, your mileage may vary and it might get fixed in the nearest future, but be cautious nevertheless. Just a few fun facts.