His semblance matches his inner beauty: Calus, the former Emperor of Cabal, is the main antagonist of Destiny 2: Lightfall. It is a fairly difficult fight, especially if you are playing the Legendary Campaign. If you are still struggling defeating Calus, this Destiny 2: Lightfall guide will help you out.
How to Beat Calus on Legendary (Boss Cheese Tips)
In the first phase, do not become Strand Empowered straight away. You should definitely use your Supers before becoming Strand Empowered if you want. Calus will simply stay in the middle and shoot Darkness Orbs at you. You can simply shoot these with a Primary or just dodge. Both things work.
There will also be some Psions in the middle but they do not pose a threat. Periodically, Calus will spawn in Shadow Legion in three platforms around the area. These are not a priority but you should consider dealing with them whenever you have a moment.
After damaging Calus a little, he will spawn a Tormentor. If you have decent DPS, feel free to ignore it altogether. Otherwise, things like Tractor Cannon, Suspend, Blinding Grenades, etc. Other than that, just keep on whittling away at Calus’ HP until he transitions into the second phase.
In the second phase, Calus will get a little close and personal. Lucky for us, his HP is not even close to what he has in the first phase. Fusion Grenades, Osteo Striga, Anarchy, Witherhoard, etc. are excellent for the second phase. You should also consider using the Grappling Points across the arena if you are struggling.
There is also a way to cheese Calus if that is your thing. However, be warned that it takes a lot of time and you are better off just defeating him normally if possible. For those of you who are interested, here is a video link that has all the details:
This is how to beat Calus in Destiny 2: Lightfall. If you have any other questions, be sure to let us know in the comments section below!