Say I have Optimus Prime, Hero on the battlefield. I cast Phyrexian Metamorph, and choose to make it enter as a copy of Optimus Prime, Hero. The legend rule triggers, and I choose to put Phyrexian Metamorph into the graveyard. What happens next? I believe there should be a death trigger which returns Phyrexian Metamorph to the battlefield (it cannot flip over), and I can again choose to make it enter as a copy of another artifact or creature.
Relevant abilities:
Optimus Prime, Hero:
When Optimus Prime dies, return it to the battlefield converted under its owner's control.
Phyrexian Metamorph:
You may have this creature enter as a copy of any artifact or creature on the battlefield, except it’s an artifact in addition to its other types.