How I dealt with clones: I killed them. I didn't run away from them / hide till they despawn.
As soon as diablo shadow vanishes, I pop smoke screen so my clone's initial attack doesnt hit me. Then I stutter step + attack side ways (Perpendicular to the direction my clone is facing) whilst spamming my smoke screen button. I make sure I am a good distance away using my initial smoke screen: too close = impossible to dodge the projectiles. Just gotta keep moving in a zig zag perpendicular to where the clone is shooting + keep spamming smoke screen. I used nether tentacles to kill them so usually took about 2 smoke screens per clone (2-3 nether tentacles pretty much killed them for me). I kill the clone before the boss shadow re-appears, so didn't really have to deal with both at the same time. The shadows spawn at: start, 66% and I think 33% (or a bit lower).
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