I think that tuning the difficulty of a fight is the hardest thing about being a GM, as much in 4e as in other editions, perhaps more so. Once you hit the paragon tier, a party that decides to unload on a boss can rack up a staggering amount of damage. Once the players realize that they’re facing a boss and flip that switch there’s lots that can go wrong and not much that can go right. In these high-tension moments, every miss is a catastrophe, every gotcha a disaster. I ran one of those encounters tonight and while some of what happened can be attributed to the fact that I haven’t felt well all day, I feel that the disconnect in expectation was what spoiled the mood of the encounter.
Keep in mind that this the last encounter of both the dungeon and the level. The characters are nearly fresh coming in and they have access to a relic that allows them to give Resist 15 all to one party member at a time.
I ended up making two on-the-fly changes to this monster. First, I just got rid of Second Wind. It wasn’t really my idea to begin with. I included it because it appears on a fair number of liches. Second, I had interpose stop working when the monster became bloodied. This was easy to justify because it already has stuff that stops working as it becomes more and more damaged.
What I found really frustrating was the hangdog attitude that crept in once the players realized just how straight-up hard this encounter was going to be. Despite the previous encounters having a lot of weird mechanics and complications, this was the only fight that they complained of being work, which I guess is a fair statement, but it doesn’t address the fact that sometimes an encounter is supposed to push you. Really, really push you.
Edit: I was talking to Nigel on Facebook and I learned something that I can use in future boss encounters. Interpose isn’t bad because it’s too powerful, it’s bad because it takes one person’s turn and makes it complete crap. The Paladin and the Barbarian did an excellent job of avoiding this mechanic, but even their turns were muted by the ongoing need to not have their turn flushed down a toilet.
I’m thinking that the following might be a good change:
Interpose * At-Will
Trigger: Ostellos is damaged by an attack.
Effect (Immediate Interrupt): Ostellos takes 20 damage and a minion within 10 becomes the target of the attack instead.
This retains the “brinksmanship” aspect where the characters can try to get him to use the power so that another character can land a heavy blow, while not completely negating an attack.