Walkthrough for Cure For Most Of What Ails You of Red Dead Redemption: Undead Nightmare.
1. Travel to left side of the Map marked with U to meet Nigel West Dickens at the Fort Mercer, under Rio Bravo.
2. Dickens will ask you to bring him five Violet Snowdrops and five Desert Sage.
Desert Sage: You can find it just in left side of the map in a place called Gaptooth Ridge northwest of Fort Mercer.
Violet Snowdrops: Grows only in snowy places. Go to Tall Tree on top right of the Map.
3. Get back to Dickens after finding five of each. He's in the W mark in left side of the Map at the Repentance Roc.
4. After talking with Dickens, he will ask you to bring him three Nigel's Charge.
5. A small area of the map will be marked green, on right side of the Rio Bravo. Go there and pick up the parts.
6. Go back to Dickens at the W mark.