To get the Reduvia Dagger in Elden Ring, you must defeat Bloody Finger Nerijus. Bloody Finger Nerijus is an NPC Invader that you can find along the Mirwater River.
The easiest way to find him is to use the bridge east of Gatefront Ruins that crosses the river. From the bridge, head north up the river until you encounter him. Be wary, as you will meet pockets of undead that will attack along the river.
Related: How to get the Twinblade in Elden Ring
Once you see a cave opening with a campfire on your left, Bloody Finger, Nerijus will start his invasion. His attacks cause a lot of blood build-up, so this can be a tough fight if you are not ready for it.
An easy way to defeat him is to keep out of his reach while waiting for an NPC hunter to spawn. This NPC is called Bloody Finger Hunter Yura and will assist you in the fight.
Let the friendly NPC do most of the fighting. Swoop in for backstabs or easy hits while Bloody Finger is distracted. Once Bloody Finger Nerijus is dead, you will acquire the Reduvia Dagger.
The Reduvia Dagger has a decent passive blood loss build-up skill and scales with Strength, Dexterity, and Arcane. You will need at least 5 Strength, 13 Dexterity, and 13 Arcane to wield it.
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