Killing black unicorns
|Tier 50+ melee weapons|
300 × Unicorn horn (902,100)
Black unicorns always drop unicorn horns, worth 3,007 each. The best place to kill them is in low-level Wilderness, although this is dangerous because you could be killed at any time. For that reason, it's recommended to only go into the Wilderness with one item -- your two-handed weapon. If you use Magic or Ranged, use items that do not require separate ammunition -- polypore staff, mystic air staff, or the crystal bow. Have the Protect Item prayer ready so you can protect the weapon if someone attacks you. Although Unicons and Black unicorns exist in other locations the aforementioned Wilderness location is the only one with a high enough number of them to make a profit.
The unicorns are found north of Edgeville, in level 18-20 Wilderness. Walk north from Edgeville to reach them, and start attacking -- they only have 1,200 life points so they should only take a couple hits to kill, another option would be to teleport to the wilderness volcano lodestone, which is very close to the black unicorn area. Pick up the unicorn horns, repeating until you have 28 total. The unicorns may do a small amount of damage to you unarmoured, but not enough to require food. When your inventory is full, teleport back to Edgeville using either the lodestones or an amulet of glory, and repeat.