Harpoon

The Harpoon is a free-to-play Old School RuneScape item — “Useful for catching really big fish.”. Its Grand Exchange buy limit is 40 per 4 hours. Right now it buys at 80 gp and sells at 99 gp — a net margin of 18 gp (22.5% ROI) after the 2% Grand Exchange tax of 1 gp. High alchemy yields 3 gp.

To flip it, place a buy offer near 80 gp and a sell offer near 99 gp; the spread minus GE tax is your profit. Confidence figures are model estimates from live OSRS Wiki prices, not guarantees — flip responsibly.