I was hoping to power through the Amber Temple in a single sitting. As usual the murder hobos have their own pace, and I have no problem watching them make tactical errors.
The first mistake was the party didn't properly dispose of the Flame Skulls once they vanquished them. One short rest later, and I had them stalking the party a bit. On top of that, they provoked a yugoloth. The Ranger went off on his own briefly and that's when I dropped those 2 doozies on them at the same time.
Unfortunately they succeeded in defeating the Flame Skulls again, and the yugoloth wasn't stupid enough to stick around. So now they rest (smart use of Mordenkainen's Private Sanctum). The denizens of the Temple are now aware they are there and will test them to see if they are worthy of the "gifts" the dark powers may impart to them.