Posted Wed, Mar 06, 2013 by gunky
Occasionally, the dungeon master needs to correct a mistake introduced in a previous session. Characters become too powerful and no longer fear death by Hit-Point-loss, so a new form of danger must be introduced that once again gives them pause and makes them cautious. A player with a powerful magic item has been using it to annihilate his enemies at every corner, so a new enemy with immunities to that item's effects comes into play. Or perhaps the DM simply wishes to exercise his sadistic streak and punish and abuse his players. Either way, the Monster Manual provides the means to achieve these ends.
A good storyteller will add clever twists to his tales to keep the audience guessing, and lazy DMs can accomplish this with deceptive monsters. Mimics look like treasure chests until they chomp off the hand that reaches in to loot them. That sweet dark garment hanging on a hook by the door might not be a real magical cloak, but a Cloaker that will attempt to strangle and eat anyone attempting to wear it. Those perfectly normal-looking stalactites? Some of them are alive and will impale you when you walk below them. That puddle of water? Actually it's just water... but at the bottom is a crystal-clear slime-monster indistinguishable from the puddle above. Even perfectly ordinary clear air can be hostile if an Invisible Stalker is in the neighborhood. The Monster Manuals give the DM loads of tools to help him be a player-hating dick.
A number of monsters have particularly deadly, impairing or deleterious effects on the players. Instant-death attacks have become less common over the years, but the Banshee's wail has always been instantly lethal. Even worse than that was the Rot Grub, a worm that would burrow into the victim's flesh until it reached the heart, killing the host. This was particularly cruel because the victim needed to make a successful Wisdom check to even notice the infestation, and the "cure" involved burning the worms out with fire... within the first 6 or so rounds of infection. After that, the only solution was a Cure Disease spell. 4th Edition rules have more or less eliminated the instant-kill monster, but these guys are nasty even in their nerf-y 4E bodies.
There were only ever a small handful of monsters with instant-death attacks. But there are loads of monsters with incapacitating attacks - especially petrification and paralysis. Medusae, Cockatrices, Basilisks, Catoblepases and Gorgons, among many others, all have attacks that permanently turned their victims to stone. Paralysis is another very common type of incapacitating attack occuring in loads of monsters (including the previously-discussed Gelatinous Cube). Powerful demons, devils, dragons and other large beasties have a fear aura, which can cause anyone just looking at them to freak out and flee in a panic.
One of the douche-iest DM-Revenge monsters ever created is the Rust Monster, a creature that destroys any metal objects it touches. Fighter types with razor-sharp enchanted swords and bunker-like plate armor, who can take on most any powerful foe without fear, are reduced to quivering bowls of angry Jell-O when faced with a Rust Monster. In older editions, the Rust Monster was relatively peaceful, only interested in consuming the metal worn and carried by adventurers and not in their meaty bodies. 4th Edition has beefed the Rust Monster up a bit, giving it a stronger bite attack and increased movement speed from 3rd Ed, but nerfing the rust effect so that it only happened as the result of a successful bite attack.
Mimics have already brought their brand of cruel deception to Neverwinter, but hopefully none of these other creatures find their way in. Avoidable instant-death attacks are to be expected as a part of boss fight mechanics, and temporary, non-lethal incapacitating attacks are a major part of any game system using magic. But any kind of balancing issues that might otherwise require the introduction of a Rust Monster can be avoided by standardizing gear and loot drops, which is sort of central to any MMO.