I’ve alluded to phased bosses a few times, but I haven’t gone in-depth about it. A phased combat encounter is any encounter with multiple stages as part of the same fight. These stages must be mechanically distinct; a knight who becomes wary of attacks of opportunity isn’t entering a new phase, but a knight who switches to a heavy weapon or descends from horseback may be. The stages must all occur in the same encounter, but they don’t necessarily have to include the same monsters or even the same battlefield. As long as you compress multiple thematically-linked fights into one combat without a significant break between them, you probably have a phased encounter.
Despite the prevalence of phased bosses in other media, D&D doesn’t have a lot of information about doing it. I think that’s because it makes the math really hard. D&D balances encounter difficulty based on Challenge Rating math or an XP budget, and phased encounters don’t interact nicely with either. If you give your players an encounter with a 200-XP phase and a 300-XP phase, it’s harder than giving them two encounters because they don’t have the rest in between, but it’s easier than one 500-XP encounter because they’re not dealing with it all at once. D&D doesn’t like taking carefully-crafted mechanisms and adding a rule that says “and then you just wing it, we guess”, so there’s little literature on phased encounters. And that’s a shame, because good phased fights are among the most flavorful, exciting, and interesting fights you can give your players. Continue reading