Teshar triggers, returning Scrap Trawler from your graveyard to the battlefield.
Activate Delif's Cone by tapping and sacrificing it.
Activate Yahenni by sacrificing Scrap Trawler.
When Scrap Trawler dies, it triggers, returning Delif's Cone from your graveyard to your hand.
Resolve the Yahenni ability.
Repeat.
This clever loop transforms a humble artifact like Delif's Cone into an engine for endless sacrifice and resurrection. When you cast the Cone, Teshar, Ancestor's Apostle uses its historical synergy to yank Scrap Trawler right back out of the graveyard. From there, you tap and sacrifice the Cone, then let Yahenni, Undying Partisan consume the Scrap Trawler as fuel. That death triggers Scrap Trawler's passive ability, pulling the Cone safely back to your hand so you can cast it all over again and repeat the cycle indefinitely.