Couple suggestions at random here:
- All mobs invulnerable to the effects of Cleric's SOG (Seal of the God), I've seen it used countless times to prevent people from killing mobs, or to even kill parties or newbies.
- Random spawn times of Mini WB (Decieter's, Snow Bear, Sutrixx, Stiren General, Hum Hum, and co) Regular WB (Minion of Death, Cenminator, Frostagelion, etc.) and Harpy+EPW WB (Harpy, Death Knight, Apocalypse, Atlantean, Crawler, etc.). That way people can't sit and time manage bosses. (some who know me would find it ironic that I suggest this, I think it would be a good idea). I'd give just an idea, say, a variation of 10-20 mins per spawn from 90 mins, or a completely random time between 60 and 120 minutes.
- Faster spawn time of 89 culti mobs (Frost Fairy, Tangleweed, Toras, Burning Spirit). At least two of them (I think Frost and Tangle) have around a minute and a half spawn time. I think it should be easy to decrease this down to like.. 5-15 seconds with zero effect on the game, other than people completing culti several minutes faster.