What wishes were the shadow dragons of dragon-ball z gt made of

They were a ball of negative energy from wishes to like revive the dead kill buu stuff that was negative and to many of these were bad so the shadow dragons were a fail safe in case a race couldn't handle problems on its own. So basically they eliminated races that are doomed sorta speak.
***This is why the Namekians almost never use their set of DB's.
**Hope this answers your question.
*LOL:)