EN5ider 182: Behold My True Form: Creating Evolving Boss Monsters (5e)
It can be tough to run a solo boss encounter when the PCs have it outnumbered 6:1 with actions. The focused-fire principle often means that such encounters are embarrassingly short¸ unless you just make the creature a ridiculous bag of hit points. This article talks about ways to make your solo boss encounters more challenging¸ and more interesting¸ by giving it special traits which kick in at different times.