Bag of Holding

A bag of holding holds far more volume on the inside than it appears on the outside, and will weigh only a fraction of its content's mass. It's explicitly named "bag of holding" for Dungeons & Dragons, but you'll find something similar in any rpg that has magic, or sci-fi that might as well be magic. It's just too damn useful not to have. It is a must-have item for dungeon delvers and murderhobos, so they can stop worrying about encumbrance rules (gold coins in D&D used to be 1/10th of a pound) and deny they have a hoarding problem just a little longer. It may have been made worse by early adventure video games, where you had to collect everything because you didn't know what might be a piece of a puzzle later.

Since it is such a common item for adventurers, and breaks physics in a very simple way, it is a lovely tool for gamebreaking.

The Necrons love this kinda stuff, what with their pocketdimensions and doors to infinity (and beyond). They even have a Pokéball for their lords and overlords, if the happen to encounter some dude they just really want to have in the collection.

Shitcannon of Holding

Let's say you have a bag of holding, 1,500 pounds weight limit. In feudal lands you can easily acquire 1,500 pounds of cattle shit to fill the bag completely.

Falling objects in D&D do 1d6 damage per 200lbs per 10 feet they fall. A falling object will accelerate to ~15 metres per second after 40 feet of falling. Remember this for later.

A human's normal movement rate in Dungeons & Dragons is 30 feet per round (6 seconds). If the human took the 'Running' feat, they can sprint to 5x their normal movement speed, or 150 feet in one round. With a Haste spell in effect, that is doubled to 300 feet in one round. 300ft / 6seconds =~ 15.24 metres per second.

So. One guy holds open the bag of holding in outstretched arms, pointing the mouth at some evil wizard. Other guy gets Hasted, runs at full tilt at the back of the back. This will easily invert the bag, violently ejecting its contents at the imparted speed. The target the bag was aimed at will get 1,500 pounds of shit at a nice 15 metres per second, for (7.5 rounded up) 8d6 damage, x4 for the extra speed. That's a total of 32d6 of filth applied directly to forehead, more than the evil wizard's 20d6 max fireball. Average 62hp of damage, max of 192hp. No there is no metamagic feats for maximizing shit damage.

No Fun Allowed Section: but the running guy has like 1/7th of the mass of the ejected shit, so it should be travelling at 1/7th the speed even with a perfectly elastic impact.

The bag of holding negates mass for the items inside the bag, and the runner is hitting the back of the bag; laws of inertia are already being ignored before you even open the bag. If you're that upset about it, drop the shit on the wizard from a great height. Fifteen hundred pounds of horseshit is like 375 gallons or 1.7 kilolitres of volume, easily enough to bury someone.