Soul rune

Soul Rune is a members-only item on the OSRS Grand Exchange in the runes category.

In-game examine text: "Used for high level curse spells."

It has a Grand Exchange buy limit of 25,000 every four hours, a high alchemy value of 180 gp, and item ID 566.

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Soul Rune shows an active flip setup with a margin of +1 gp and 23,268,888 trades over the last 24 hours.

At the buy limit of 25,000 every four hours, max profit per cycle is about 25.0k gp — high margin with healthy liquidity.