Tormented Demons Question

Note that this is only for people who have experience with Tormented Demons. If you don't, then please don't bother.

Alright, I was just wondering how some people get like, 20 kill trips at Tormented Demons. I've seen high levels do an entire demon without taking a single hit. How do they do this? I mean, if everything worked like it was supposed to, I could see how that would be possible, but there are a shit-load of complications.

Some examples:
Demon doing the "roar" twice in a row
Demon doing the "roar" and then not switching attack styles
Demon roaring and then nothing happens

How do you know what it will do when it does any of those? They mess me up a LOT and I'm almost always getting hit by 250's every time he does something like that and I miss a prayer switch.

Is there something I don't know about them? Because all I know is that when they roar, you switch prayers and switch back and forth between Protect from Magic and Protect from Ranged while standing in a safespot and switching your weapons depending on which protection prayer he is using.

Thanks for the help.