If a player controls Graveyard Busybody and there is an Over My Dead Bodies in play, what happens due to a creature being in both player's graveyards. In particular, could a creature with vigilance attacking it's owner from it's owner's graveyard still be used by that owner to block, could it block itself?
Graveyard Busybody: All graveyards are also your graveyards.
Over My Dead Bodies: Creature cards in graveyards can attack and block as though they were on the battlefield