Opal Rat Arena WIP

Rush Opal Acorn. The CDR is high enough to save your life and it's half of what is vital to come online.
Golden Bow is second.
Opal Acorn gives Dart the ability to hit with 6 Basic Attack hits. Golden Bow gives cleave on Basic Attack hit. Best case scenario, a Dart will hit five enemy gods, each one being hit by the basic attack and up to four cleaves. This can also crit.
If there's a situation where Opal Acorn is not finished but you can outright buy a throwing dagger, do so. Your dashes will not be very effective yet, but the small cleave will help farming up the two core items.
Warrior's Tabi or Reinforced Greaves are the shoes of choice. Up to taste, and these can also be purchased before Opal Acorn or Golden Bow.

Much like Mercury, Deathbringer is the turning point when Ratatoskr becomes done farming.
Jotun's is a solid item if there are no better situational items.
Heartseeker is in the same boat. It is worth noting that Heartseeker can build and expend stacks with Opal Acorn Dart.