|Mort the Cleverly Named|
And "conserving resources" is not the same as a castle on an invasion plan that has more than two levels worth of encounters and will likely take days to clear unless you are tricked out enough to (without rest, two levels down) beat the boss and three captains who are stated to (through mechanisms I am not clear on) join him in the final battle.
It straight said this would be a "virtually unwinnable encounter" or the like and you should discourage PCs from fighting the leader without taking them out, but I couldn't find any mechanisms it set up to do that. I can certainly make up those mechanisms, just like making up how the castle reacts to getting to a populated area or the piles of corpses left by PCs hitting and running over a few days, but because I can fix it doesn't mean the adventure is particularly useful to start, and as I said from the start seems more like a "set piece" than a proper "adventure" meant to be played. I'm not particularly interested in paying money for an adventure I would, in the course of entirely reasonable and likely actions by players or enemies, end up having to mostly write myself.
I was hoping there was something specific I had missed, but otherwise I don't think this is an adventure I'll bother picking up.