Board Thread:Show-Related Questions and Answers/@comment-33243493-20171027000036/@comment-25926288-20171027003814

Generally speaking, they have to do what the person commanded them to do.

On a more wordy note:

Depends on the tethering spell, power level, will power, etc. However, in all cases, but one, have they resisted.

In all but one case, The Dark One has to fulfill the command. They can twist the words and meaning, similar to a genie, but they still have to do it. There's really no hypothetical where they resist.

In that one case where resistance happened, the command was going to follow through eventually. So, they'd only be able to resist for a few seconds.