Action Bomb: The Conjurer can summon Bombers that can be loaded with up to three different offensive spells.
Amazing Technicolor Population: Some characters can have strange colored skin, but due to customization, you can choose whatever skin color you want your player character to have. Even green.
An Axe to Grind: One of the weapons available for warriors. There are also the Ogre Axes used by Ogresses, which do more damage, but are very flimsy.
Apathetic Citizens: Destroy their stuff, steal from their homes, and town citizens do nothing.
Breakable Weapons: Both armor and weapons wear down on use and have to be fixed by a smith or replaced. Also, while playing as a Wizard, one may have a little fun by casting AOE spells at friendly NPCs to break their armor and strip them naked.
Bubblegloop Swamp: The Dismal Swamp and to a lesser extent the swamp outside Grok Torr.
Chain Lightning: A Wizard class staple. As long as the user stands still after the (short) casting period, mana will flow into electric damage points at a 1:1 ratio. Cheaper than any other spell for clearing Goddamned Bats.
Cool Down: All special abilities, be it spells or Warrior's skills, had a short cooldown period, though the spells were additionally limited by the caster's mana supply.
Cosmic Keystone: The Staff of Oblivion (possibly a Game Breaker, as once you get it, it's usually not necessary to use any other, breakable weapon).
Death Ray: Death Ray and Force of Nature, two very powerful spells. Also, the Staff of Oblivion.
Development Gag: Kinda. The game persistently nudges you towards playing as a Wizard, including giving them the largest amount of abilities and the best ending (to say nothing of The Stinger, which challenges you to finish the game as a Wizard unless you just did). This is because Nox was originally conceived a "wizard battle game" and the other two classes were added later in the development.
Dismantled MacGuffin: The Staff of Oblivion is split in four parts: the Halberd of Horrendous, the Heart of Nox, the Weirdling Beast, and the Orb.
Eleventh Hour Superpower: The Staff of Oblivion, natch. An unusual example in that, while it handily vacuums up any regular enemies or even minibosses that come at you, if you rely solely on it during the final boss fight you will still get curbstomped. To beat the final boss you actually need to use a combination of the Staff and your built-up spells/skill powers.
Fireballs: Many. High-power projectile used mostly by Wizard characters, and by the very occasional mook.
Fire Keeps It Dead: If a zombie is killed by a non-fiery weapon/spell, the only way to prevent it from resurrecting a few seconds later is to immediately hit its corpse with a fire spell (even the weakest one will do).
Multiple Endings: Uniquely, the ending you receive is determined the moment you choose your class at the beginning of the game. They are still worth playing for, though... The Warrior gets the Normal End (Jack kills Hecubah and returns home), the Wizard, the Good End (Jack "purifies" Hecubah and makes her his girlfriend), and the Conjurer, what may be perceived as a Bad End, since he kills Hecubah but it doesn't bring him back to Earth.
Regenerating Mana: The game had "mana stones": stationary glowing pillars that quickly restored your mana if you stood nearby. Particularly when playing as wizard, controlling large conglomerations of mana stones was essential to winning long battles.
Spell Crafting: Wizards and conjurers can create custom traps (stationary ones for the former, living summons for the latter) with up to three spell effects that they already know. Once a trap is triggered by a enemy's proximity, all three spells are unleashed at once. On the downside, creating a trap requires enough mana to power all three spells, which is expended at once, without a chance to regenerate. If you don't have that much, you can't create that trap.
Sucking-In Lines: Some spells do this while powering up, such as Force of Nature.