Force Field + Cove

On Day 5, Rarran was able to find a Force Field. With the effect: "Deal Damage equal to your Shield.", it made the perfect match with the Cove he found on Day 3.

The Cove is one of the easiest Shield items to scale since it only needs you to sell items. So as long as you don't become super poor throughout your run, you can constantly feed it.

Make sure to use items like Shovel (what Rarran used) or Fishing Rod to continually generate free items that you can sell and build up its value.

These two items offer your main offense + defense engine, now you just need to speed it up to make it cast ASAP.

Force Field

Cove

Captain's Wheel

The Captain's Wheel is an ideal choice to put in between Force Field and Cove as it not only Hastes adjacent items on a cooldown, but it also automatically casts when a Large item is used.

With both of those items being Large and fast-casting, your engine is going to be casting very often.

Since this build's core is pretty straightforward (the hardest part is finding the Force Field), the remaining Small item slots and Skills are very flexible.

The choices that Rarran prioritized focused on buying him more time in the form of crowd control or ramping up his Force Field + Cove engine.

Clamera (instantly Slows to buy time for your engine's first cast)

Silencer (Greatly decreases the Force Field's CD + flat damage increase)

Big Numbers (gives massive Crit Chance increase to Force Field + Cove)

Left Eye (since damage is based on Shield, it's better to place Cove on the left)

Righty Tighty (gives Force Field crowd control)

Stunning Strike (gives a massive 10 second Freeze on an item)