Situation:
Player A attacks with a {Rhox Pikemaster} equipped with a {Scythe of the Wretched} and a {Mask of Avacyn}
Player B blocks with a {Rusted Relic}
The question is: Does the {Rusted Relic} return to the battlefield after it dies?
As I understand it, the scythe would trigger because at the point the {Risted Relic} reaches the graveyard, it enters as a creature. When it enters the battlefield again, it checks metal craft and if the criteria is not met, the scythe will not attach.
Relevant ruling:
12/1/2004 If the card isn't a creature when it comes back onto the battlefield, then Scythe of the Wretched won't move onto it.
For clarity's sake, the operation occurs like this.
{Rhox Pikemaster} deals first strike damage to {Rusted Relic}.
{Rusted Relic} enters the graveyard as a creature, triggering {Scythe of the Wretched}.
{Rusted Relic} re-enters the battlefield for the opponent, and the game performs a static check to confirm if Metalcraft requirements are met.
Depending on that static check, {Scythe of the Wretched} equips to the new creature.
Hope that helps.