Diablo 1 HD Hellfire Mod | Awake

With ranged characters, right after you meet diablo and he comes after you if run behind the wall (the one of the corridors) there are some positions you can stay that makes him inactive (he doesn't go after you, he just stands as if he doesn't notice you), even though you attack him with ranged weapons or spells.
And this also happens with some other bosses and normal monsters.

Yes, thats the way of ur technique. But once i had same situation and he stayed in my firewalls and guardians his life was about 15% then he teleports to his main place and got again full life.

Yes! That's right! he sometimes does that but not always. I noticed if you keep moving and keeping your char far away and out of his sight a lot he does that. But he won't do it necesserily if he is in that state of recieving damage and standing.