Magic boxes are used in the capture of imps using the Hunter skill. They require a hunter level of 71 to place. Successfully catching an imp gains 450 hunter experience. The boxes can be baited with Beads, which makes them slightly more attractive to imps. If, while deployed to catch an imp, a magic box fails to catch one, it will be labelled Magic box failed until it deactivates or is picked up.
They can be bought in the hunter shop in Yanille and Nardah for 720 coins. When an imp is caught, the magic box will become an Imp-in-a-box (2). The imp will agree to take two items or stacks from the player to the bank in exchange for its freedom. However, they can randomly refuse and will always refuse to do so past level 30 Wilderness.
Imp-in-a-box
Imp-in-a-box can be used by right-clicking on one and choosing "Bank Imp-in-a-box", then a window will come up where the items to be sent to the bank can be selected (be careful to not click twice quickly, because items can move after clicking on the first one). Alternatively, simply use an item on the box for it to be send to your bank. This method is a quick way for players with higher hunter levels to quickly bank items in for example PvP areas.
Note that when the box can be used to send two items to the bank it will be labelled Imp-in-a-box(2); when one has already been used, it will be labelled Imp-in-a-box(1) and when both have been used, it will revert to Magic box.
For high security transport of items, transport items to the bank with imp boxes and, as the boxes become empty, use your imps to send them to the bank using unused imp boxes. this way, the resources are instantly banked, and all but one of the expensive magic boxes are also banked, ready to be refilled. you can then fill your inventory, and bank as normal.
For large volume resource collection, combine a beast of burden familiar with your imp boxes. Send your resources and empty imp boxes to the bank, then fill up your familiar, and your inventory and travel home. This will allow you to transport: 28 items in your inventory + 28 items banked by the imps (+banked boxes), + your familiars cargo space worth of items. If you have a war tortoise, that's another 18 spaces for a total of 74 items per trip. Using a pack yak, that's another 30 items, for a grand total of 86 items per trip.
For quest items that cannot be handed to a familiar, the method above still works. Simply hand your empty magic boxes to your familiar until it is full, then ship the remaining empty boxes to your bank with imps from occupied boxes. In each case, the sums come out the same. Imps either take one item and one magic box home, or the box is handed to the familiar, and the imp carries 2 items home. 84 phoenix feathers or nightshades per trip is a great improvement on 28. (The yak can hold all of the boxes, but 2 spaces will be left over that cannot carry quest items home.)
When collecting valuable items, one tactic is to just drop the magic box once the banking of the imp-in-a-box has been used up, as the profit from the items can greatly exceed the cost of the box. For example, Red dragons drop Dragon bones and Red dragonhide, each of which is worth several thousands of coins per item. It thus can make sense to drop the magic boxes when emptied, in order to carry more bones and dragonhides.
Shattered heart
When collecting strange rocks for the Shattered heart activity, the random check to see if you get a strange rock is performed when you pick up an occupied, or failed imp box.
To maximize the chance of gaining a rock from each imp, set up as many boxes as your hunter level allows, and reduce your effective hunter by any means available. Try using the level-lowering cold outside of the Godwars Dungeon to reduce your level, do not smoke or bait the trap, and stand as close as possible to the traps. This should ensure the maximum number of failed traps per imp, vastly increasing the chances of getting a strange rock.