So, say you had {Venser, the Sojourner} and a {Conjurer's Closet} on the board, with some random creature. Now say you decided to use Venser's first ability on that creature to flicker it. Since Venser's ability hits when the turn ends, as does the Closet, which goes off first; the Closet's flicker, or the end of Venser's flicker?
you choose. they both happen ay the beginning of the end step.
This doesn't work with only one creature.
Here's what happens:
During your main phase, you Venser away a creature.
At the beginning of your end step two triggers will be put on the stack - Venser's and Closet's.
Even though you can decide the order of the triggers, each one needs a target when you put it on the stack, otherwise you can't put it on the stack in the first place.
The Closet can't target the creature until after Venser's ability resolves.
Clear as mud?
Just like how two closets can't target the same creature
They can target the same creature, but once the first one resolves, the second one loses it's target.