Holy shit. A WMD for the D&D world.

never let engineering students design magic items

i’m pretty sure this would be most effective in naval combat, to hull big ships. a regular arrow will kill someone plenty dead in small skirmishes. a regular cannon ball, discharged over a battlefield, is fired at a nearly horizontal angle, so it takes out as long a line of combatants as possible while skipping along the ground, and would probably do just as much damage along that line as this device, rather than going off on the first dude it hit and taking out just one ring, while whatever load of rock and rubble a catapault would dump onto a battlefield would take out a much wider blast radius than just 10 feet. but a 10-foot diameter scoop taken out of the hull of a ship is a pretty big deal in any universe. 

if you stuck with arrows to deploy this device, it also wouldn’t be anywhere near as heavy as the 12000 pound cannons required to fire a six pound cannonball, and there’d be no dangerous recoil or risk of explosion on the firing ship. but a professional archer with a longbow’s range would only be about 400 yards (though very accurate) while a six-pounder could go up to 1500 yards (though less accurate). so it’s a toss up which method would be better, unless you’re working in a world without gunpowder, in which case your ships would be closing in much more closely to exchange crossbow/arrow fire, throw flaming crap, or try to ram and board, and you’d do just fine with tension-launched rift devices.

come to think of it, were these things to be invented in a time before gunpowder, the ensuing arms race would be all about range, not explosive power or accuracy: whoever could accurately hit the other guy from furthest away would automatically win. we’d be seeing some really interesting sea-trebuchets in a generation…

you could, of course, just manufacture a lot of sea mines, and dump them.

considering how expensive portable holes and bags of holding are to make, i would save this for targets that are essentially immune to regular damage. there are an alarming number of them in the d&d world.

re ships, tbh, in a high-level game, when we did naval warfare the difficulty was keeping any of the ships afloat. for instance, our sorceror pioneered a move we called “fuck these six cannons in particular.”

and then there were the enemies you’d unleash all this firepower on and they’d pretty much laugh it off because they’d layered on 9 kinds of immunities and 20 points of damage reduction. but nobody is immune to a bag of holding implosion.

In a world where these things somehow catch on (disregarding prices for a moment), an interesting complication arises: by the rules as written, this is not an Arrow of Total Destruction. It’s an Arrow of Greater Banishment. See, when it says it opens up a rift to the Astral Plane and sucks everything through within 10 feet, it’s not being metaphorical. Everyone caught wholly in the blast radius of one of these arrows doesn’t die, they’re just sucked into the Astral Plane, which is hard to leave but other than that is actually a relatively hospitable place to live compared to most D&D planes of existence: a vast, silvery sphere of endless sky, with subjective gravity (”down” is where you want it to be) and total freedom from the ravages of time (age, hunger, and thirst need not apply).

A battlefield where these are used extensively leaves a lot of confused immortal refugees on both sides just hanging out in the corresponding Astral location, possibly with no real reason to continue the fight. A war where these are used extensively leaves a whole multicultural population stranded there.

aaaaand you just gave someone their campaign setting. 😀