The bosses in Diablo 4 aren't supposed to be easy to beat, but there's one fairly early on in the game that's quite possibly driving you mad. At the end of Act 2 you come up against Astaroth mounted atop the Amalgam of Hatred, aka, a triple headed giant demon dog.
You've already faced the Amalgam of Hatred in the events preceding the final Act 2 boss fight, but this is a whole different kettle of fish. There are multiple phases, and in each one Astaroth can deplete your life almost entirely with a single hit. It took me three attempts to defeat him (score one for not playing hardcore) so I'm going to offer some advice that may well save you from banging your head against the wall.
