Goblin Welder

Oracle Text

T: Choose target artifact a player controls and target artifact card in that player's graveyard. If both targets are still legal as this ability resolves, that player simultaneously sacrifices the artifact and returns the artifact card to the battlefield.

Card Rulings

8/1/2008 As the new wording makes clear, both targets must still be legal as the ability resolves in order for it to do anything. If either one or both has become illegal, nothing gets sacrificed and nothing gets returned to the battlefield.