In
old versions of
Nethack, a
technique used by
munchkins to get all the
good stuff.
It depends on the effect of polymorph wands and spells on items lying on the ground, which (perhaps uniquely in Nethack) changes them into semi-random other items of the same general category (i.e., armor changes into other armor).
The abuse is that players can collect all the useless junk they've found in 20+ levels of play into a huge pile and zap a wand of polymorph at them. Presto! They now have a pile of lots of other stuff, some of which should be useful. Nethack long ensured you couldn't get wishes this way, but any other randomly-produced non-artifact item could appear this way, and in particular, you can get more wands of polymorph and ways to recharge the wand(s) you already have. Also you could dump hundreds of rocks into the pile and turn them into gems, which is not really so abusive for being able to sell them and get enough gold to buy anything, since high-level characters reach this point anyway, but it allows munchkins to get extremely high finishing scores, since the value of all the gems counts in your score.
Modern versions of Nethack prevent this abuse by only polymorphing a few items from any one space. To punish the munchkins, if you attempt to polymorph a really big pile, some of the items merge and form golems that come and attack you.
In a couple gammas of
ADOM a while back, there was a weak sort of polypiling possible. ADOM doesn't have a general polymorph ability, but after
TB implemented a feature that made things dipped into
potions of raw chaos turn into random objects of the same type. Bundles of items becomes bundles of the same number of items of a new type. Reportedly, even artifacts could be produced this way; somebody claimed to have dipped a bunch of daggers and pulled out a bunch of one of the artifact swords; making it produce only one of an artifact was the first thing fixed.
Potions of raw chaos are fairly rare, though, and dipping an item uses up the potion, so this wouldn't seem like too much of an abuse. However, every character who gets decently far along in the game finds a particular cursed artifact that it changes any potion it is dipped in to a potion of raw chaos. Advanced characters might have accumulated 30 or more potions they have no use for (more, if they go back and clean out all the shops in the game using the overflowing piles of gold available in the depths of the dungeon), so they could get quite a few chances at creating that one item they need.
When this effect became widely known, it was adjusted it the next gamma to provide "suitable" counter-effects: no more artifact production from potions of raw chaos, a limit on the number of items dippable, and sometimes it doesn't work, or the potion explodes and corrupts you a bit, or you get back fewer items than you dipped, etc. This is now called chaos roulette.
You can also do this more safely with blessed potions of exchange, but they are rare and not easily created.