So DoN Osha's ability is:

Challenges: Stand Osha to remove her from the current challenge.

Pg. 11 of the FAQ says under "Effects":

All character abilities have an effect, and may be triggered whether or not the effect has any result.

If I pay the cost (stand Osha) to trigger the ability whether or not it has any effect, can I do that any time durring the challenge phase? There has got to be a reason the answer is no.

Does the "current challenge" wording in the ability create a timing restriction or something?

Deathjester26 said:

Yes. By saying " from the current challenge," play restrictions are placed on triggering the ability that not only require a challenge to be in progress ("current"), but for Osha to be participating in it ("from") in order to legally initiate the effect.

I thought it was "only" the effect, not restriction on him. But I prefer it like that,it's more balanced.