Dark crab

Dark Crab is a members-only item on the OSRS Grand Exchange in the other category.

In-game examine text: "This looks tricky to eat."

It has a Grand Exchange buy limit of 10,000 every four hours, a high alchemy value of 192 gp, and item ID 11936.

View on OSRS Wiki

Dark Crab shows an active flip setup with a margin of +56 gp and 603,876 trades over the last 24 hours.

At the buy limit of 10,000 every four hours, max profit per cycle is about 560.0k gp — high margin with healthy liquidity.