Player with high rank can start a guild raid, but believe me, it's not worth it. Game doesn't tell you how strong goblin is and of course reward is random. I wasted gold on it and all I got was some XP and few coins. Basically this entire game exists to annoy you enough for you to loose patience and spend mone on it.
After few runs I agree with others about undead bosses loot. Player should always get at least +7 items with option of turning one into +8. Now I can end up with 2 +8 bows (1 from boss and 1 from dragon chest) while I only have +5 sword and +6 shield. In case like that I have to use altar to make +7 item and I don't think I'm going to kill something like 29 white dragons with +7/+8/+6.