When Saffi Eriksdotter enters the battlefield, Cadric triggers.
Holding priority, activate Relic of Legends' second ability by tapping Saffi Eriksdotter, adding ({1} magic symbol) .
Resolve the Cadric trigger, causing you to pay ({1} magic symbol) to create a token copy of Saffi Eriksdotter.
Activate Relic of Legends' second ability by tapping the Saffi Eriksdotter token, adding one mana of any color.
Activate the Saffi Eriksdotter token by sacrificing it, targeting the nontoken Saffi Eriksdotter.
Activate Saffi Eriksdotter by sacrificing it, targeting Cadric.
When the nontoken Saffi Eriksdotter dies, the token Saffi Eriksdotter triggers, returning the nontoken Saffi Eriksdotter from your graveyard to the battlefield.