Mega Crit CL4NK Build
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Weapons
Step 1: Prioritize obtaining your weapons. Step 2: Power level XP and Precision tomes hard. (also prioritize "projectile bounces" upgrades for Revolver and Wireless Dagger to at least 4.) Step 3: Ensure you obtain luck upgrades from shrines and "Clover" item. Step 4: Keep upgrading weapons to maintain survival.
I was able to shred the Tier 3 boss with this build first try. Good Luck!