Board Thread:Theories and Speculation/@comment-30241447-20190512072419/@comment-32685487-20190512225634

Madara was an Edo Tensei when Obito revived him, it replaces his Edo Tensei body with a real body. I think in order to bring back somebody who has died years ago you can only revive that one person, but if you want to revive multiple people they had to have died recently. At least that's how it seems to be. Also Rinne Tensei will kill the user once it is completed, unless of course somebody has the yang seal and heals them like Naruto did to Obito.. then they won't die from using Rinne Tensei.