Activate Saffi by sacrificing it, targeting Fiendish Panda.
Activate Woe Strider by sacrificing Fiendish Panda.
When Fiendish Panda dies, its second ability and Saffi trigger.
Resolve the Saffi trigger, returning Fiendish Panda from your graveyard to the battlefield.
Resolve the Fiendish Panda trigger, returning Saffi from your graveyard to the battlefield.
Resolve the Woe Strider ability, causing you to scry 1.
Repeat.
This elegant loop sets up a perpetual cycle of life and death, turning Woe Strider into a dedicated sacrifice outlet that triggers death and entrance triggers indefinitely. By targeting Fiendish Panda with Saffi Eriksdotter's sacrifice ability before feeding the Panda to Woe Strider, both creatures are able to instantly return each other to the battlefield. Because Fiendish Panda's power grows as it survives or gains counters—and its recursive ability can successfully pull Saffi Eriksdotter right back from the graveyard—the two form a closed loop of mutual resurrection.