This page lists NH4 bugs that were unbalanced, crazy or weird enough that we may some day want to add a (nonscoring) option to bring them back (so that people who missed them first time can relive them).

* Defence starting at 10: We changed from AC precisely because it was so unintuitive, but we're still using the AC scale internally, so things like this can happen. (It happened at /dev/null/nethack, too, with the bobble hats.)
* Generalized artifact naming: Turns out that for quite a while, you never got the "finger slips" message when trying to name an item to match an artifact: if the item had the correct base type, you just outright made the artifact. Sure, we don't directly have the artifact naming exploit any more, but…
* [ticket:900]: this is actually pretty funny, really (a case where a tame monster has an attack that hurts its owner, and which sort-of makes logical sense).