about bosses only being able to get slowed 50%:
decrep slows 50% but fighting a boss with decrep AND clay golem slows him more then with just decrep. So what's going on there?
According to the Diablo faqtoids site there are four different ways to slow down a monster, and they all multiply with each other:
Slow (from items or clay golem, capped at 50% for bosses/champions, 90% for other monsters)
Cold damage with chill duration (doesn't affect cold immunes)
Holy Freeze (doesn't affect act bosses)
I have thought about adding all four to see how slow monsters can get, but never got around to it. I imagine that the game would look kind of ugly if every monster was blued all the time due to a Holy Freeze aura from a mercenary. But perhaps it's worth it.
I was under the impression that skill slows (decrep, holy freeze) don't stack with each other, so hit slows 50% or more, cold damage, and decrep combined is the best you can do to slow a boss (which is super effective).