General Method Description

The sinister key is an uncommon drop from Salarin the Twisted, and can also be obtained from magpie or ninja implings; it is also tradeable. The key opens the aptly named sinister chest in the Agility Dungeon of Yanille; each time you open the chest you get an identical selection of 9 grimy herbs: 2 harralander, 3 ranarr, 1 irit, 1 avantoe, 1 kwuarm and 1 torstol. The value of the keys is always lower than the value of the herbs you get from the chest, so with an efficient method you can make money by running keys to the chest.

If you want to employ this method, you'll need to pay close attention to the herb market. Herb prices go up and down, and the price of sinister keys changes accordingly. There are times when sinister keys are hard to buy on the Grand Exchange, and other times when herbs are hard to sell, so be sure not to buy and sell at the wrong time, or you'll eat up much of your profit margin.

Efficiently running sinister keys requires the Watchtower teleport, which must be unlocked via the quest of the same name. You need level 58 Magic to cast the teleport spell, but can use tablets below that level. If you've completed the Ardougne achievement diary and set your Watchtower teleport landing point to inside Yanille, I recommend setting it back to the Watchtower if you plan to run a significant number of sinister keys.

A beast of burden is also very useful here, since you get so many unnoted herbs from each key. I recommend a spirit terrorbird at mid levels, or a bull ant if you cannot use that.

..At higher levels I recommend a war tortoise (level 67 Summoning) despite its high pouch cost, and at level 96 a pack yak obviously is the best option.

You don't need any run energy restoration with this method, because of the amount of time you stand in one place.

Tip: It takes less time to use the "empty backpack" button in your bank and then take back the super antipoison potion and another teletab, than it does to store each herb type individually.