They are hardest by being stationary. When they move it's very easy to get access to Baal and kill them. In the line of fire you're on a small bridge and Baal is behind them which means his hoarfrost rapes you from that position. ( When they are stationary )
As currently I'm expecting it to be much much easier. Anyone who wants to say otherwise feel free to post and explain.

With some map editing fire from across the chasm could be blocked off via transparent wall tiles (but I haven't really immersed myself in map editing yet... just other aspects). Shame the tentacles can't just warp to Baal whenever he teleports.

Didn't know PSN could kill him from the side. Guess it would require map editing.. that may difficult to do though unless someone knows how to do it.

It's harder if they can't move. You have to go up a long narrow hall taking shots from all three of them, and the tentacles never move and Baal rarely moves, so you have to go at it a while until Baal leaves, then kill the tentacles (else he might go back, and you return to square 1) and finally kill him.

If you can bait them out you can kill them very easily, leaving just Baal up there.

Or u can just carry a source of tele and tele across the chasm thus skipping the tentacles anyway.. If your talking about the initial early fights then yeah I see what your saying. But any char will carry a source of tele just to skip alot of the Cleft anyway.

Ok, so you're across the chasm. They can still shoot at you. What have you accomplished?

They're pretty easy either way. How about moving them farther back almost right next to Baal, add no tele/missile across the right chasm, and keep them stationary? That should make for some good times.

Shame Baal is pretty easy to lure out of there or make him tele across the chasm. I wanna see Baal stuck behind those tents spamming hoarfrost and icons all day, while those tents pummel the shit out of everyone with blood star. You might even see more than three people on the realm use Mirror's Eye.

Know what I think would be funny?

You know how some unique packs have a leash on their minions, where if you try to pull them too far from the boss you can't, because they'll run back? Imagine moving tentacles, with Baal holding the leash. Even if you pull him out, they'll still follow. Probably not possible, but funny.

+1 Good idea if possible. I almost wonder if you could skip the tentacles and just use a different model based on the Corpsefire minions.. They auto return dont they?

Like Baerk said, they will still give quests and the like. I have done it before while farting around on my own.

I put superunique versions in other areas for alt ways to get the quest. Beware though, they can get really fookin nasty. (Diablo extra fast, fanat, multishot, XYZenchanted...funfun). Plus don't they get hp and damage bonuses when you do that?

Baerk is also right on luring techniques. It's not even close to 'fool' proof.