Nerve Strike reads:
A question came up today as to whether you can target the defender that you are using as part of the cost of putting the effect on the chain.

When does the checking of targets happen? Before the cost is paid or after?

If it is before, than the effect could validly be put on the chain because there is a target defender, but upon the resolution of the plot twist it would do nothing.

If it is after, then the effect could not be put on the chain because there is no legal target because the character you used as part of the cost is no longer on the table and thus no longer a target defender.

The comprehensive rules say the following about adding effects:
This means that the targets are chosen first, and then the costs are paid right? So essentially, if one of my X-Statix characters is attacked, I could use Nerve Strike to return it to my hand?

Just checking.

Yes you can do that

Great! Yet another way to get my character count down if I need to.