Say I cast Show and Tell. I put down Angel of Despair and my opponent puts down Crystalline Sliver. "When Angel of Despair enters the battlefield, [you] destroy target permanent". Crystalline Sliver gives all slivers shroud so can I destroy slivers with Angel of Despair's ability?
If Crystalline Sliver entered the battlefield first I couldn't but if it entered the battlefield second, after Angel of Despair did, I could. But what if they enter into the field at the same time?
Also, in this same vein, what if my opponent plays Gilded Drake? Can my opponent target my Angel of Despair with his Gilded Drake?