After reading Stephen Radney-MacFarland's column "Saying Yes is a Skill", the following paragraph stood out:
...Consider this case in point. The cifal, also known as the Colonial Insect-Formed Artificial Life (I'm not joking), was a critter from the original Fiend Folio that featured a back story and a name I thought was absolutely stupid. And I was not alone; in 2000 the cifal was voted the stupidest Fiend Folio monster by the readers of Polyhedron magazine. Still, this critter showed up a number of times in my game as a swarm-of-flies devil that served Baalzebul. What did I change about the monster? Not much, just the name and alignment. It was that easy. My players were scared to death of the poor, stupid cifal, which they knew as bzazels (heck, not even a vast of an improvement on the name front, come to think of it)...Then it occurred to me that I had been doing something for years that maybe other DMs don't do, or maybe don't do often enough. I'm talking about Stat Block Masking (SBM). SBM is one of the oldest tricks in a DMs toolbox. It's easy to do, saves hours of prep time, and keeps the players on their toes. The muchkins at your game table hate SBM techniques, the role players love it. So, what is it?
SBM is where the DM uses the stat blocks for one creature, item, trap, spell, class, etc. to replace the stat block of another similar thing. The decription of the thing stays the same, but the stats are VERY different. Two examples should be enough to illustrate my point:
Example 1: The Beegguns Goblins
Goblins are easy to kill and the player characters blow through dozens of them in an evening of gaming. After a whole evening of slaughtering scores of them, complete with spell casters, traps, interesting terrain combinations, and the like, you realize that the players need a bigger challenge. But, the problem is that they are in a goblin den. To maintain internal consistency, there's a somewhat limited number of assailants you might throw at them. What can you throw at a group of Level 2 heroes that might scare them out of their wits. Then, you have an idea...
As the PCs turn the corner and see a four 'bigger', foul looking goblins coming down the hall towards them. "These 4 huge goblins come lumbering around the corner, groaning. Their bodies are covered in some kind of black oil, as are their large spiked clubs. They don't seem too happy in general, and are probably going to take it all out on you."
One of the players at the table says flatly "Oh no, these goblins look (sarcasm) scary! I charge them."
Another player metagames a bit and says, "What, they have twice the health or something? My wizard begins casting Ray of Frost."
You simply just chuckle and the battle begins. After 4 rounds of combat, the party has blown all their encounter powers, and nearly everyone has used their dailies. Action points? HAH... those are all gone. These goblins are stunning people with some sort of sap that's on their clubs, and seem like to beat on the same, stunned (panicing) heroes until they are clobbered. Plus, these guys are taking huge ammounts of damage.
Its at this point that the players realize that these are not simply "tougher" goblins; they are something else entirely.
In fact, they are Ghouls. Well... at least their stats are Ghoul stats. But, instead of claws, they use big clubs covered in somekind of toxic (to everyone but goblins) sap. Instead of being vulnerable to radiant damage, you make them vulnerable to fire damage (the sap burns quite well). In the end the PCs are fine, they mostly survive. But, they are all left wondering "WHAT THE HECK WAS THAT?"
Example 2: The Ring of Blades
Your heroes have worked hard pushing through the goblin den. Most of the goblins have either been killed or have fled to find greener pastures. In a final, last ditch effort for "survival" the goblin chieftain surrenders and offers the heroes a 'secrete treasure that will remain buried forever' unless they let the remaining tribe go free. The heroes, always filled to the brim with a lust for more lewt, agree. The chief tells the heroes where he keeps a secrete cache of coins and a few items of value. The heroes find the treasure and among they find a magic ring and a magic axe. They let the chieftain go (these heroes are real goodguys), and begin investigating the items. They seem harmless enough. The axe is a something magical, but harmless.
The ring, however, is something different. "Your skill checks are successful, and you determine it is a Ring of Invisilibility". They PCs actually failed in identifying the ring correctly and on an earlier Passive Perception check, but the game table is filled with a series of 'holy crap!" "wow!" "OMFG!" etc.
Then, one of your players adds "Wait... a Ring of Invisibility is a Level 18 item. We're a bunch of Level 2 stooges..."
"You know Mr. Metagamer, you are right! And, just as your character realizes this existential fact and holds up the ring to inspect it, it seems to unfold. Slowly at first, then faster still until the whole party are enveloped in a whirlwind of flying blades."
The ring is actually a Whirling Blades trap (p.89 DMG), and appropriate but difficult challenge for the party. You might also rule that, if they fail in disabling the trap the ring is destroy. If they succeed, they might just walk out of there with a nifty little gadget to take with them...
I've think I've illustrated my point. Statblocks can be stripped of their descriptions and applied to anything in a variety of settings, assuming you keep challenge at an appropriate level for the heroes. The trick is just to think outside the box a little and be creative. Using this technique, DMs out there will never be stuck needing a 'better' challenge in the middle of a gaming session. Players out there will also have to stay on their toes since you'll never know what to expect next...
"What the heck is that?"
"What? His mount? Oh... that's his armored heavy warhorse that was raised in the marshlands of Xuntargak. It was trained for war, and has been subject of many foul rituals by his arcanists. Good luck..." It's a heavy warhorse, but I'm using the Basilisk statblock.