When I first started storytelling the mistake I almost always made was building my own monsters from the ground up. I worried about every number on their stat card adhering to the rules and double checked my math as though Gygax himself would come smite me in my sleep if I didn't. Eventually I overcame this compulsive statistic suicide and started designing my monsters with what the players would encounter.
No matter what game your playing, so long as you create a challenge it doesn't matter if the math adds up. Monsters only need the following information when dealing with players:
I Attack the Orc. No, the OTHER Orc!
This tip is a bit on the obvious side but you would be surprised how often this simple thing is easy to forget. You don't need to give every orc NPC you ever make a unique name, but if you have a nick name for the orcs with the swords vs the orcs with the bows then its a bit easier for you and your players to identify who is being attacked during a fight. Its also a good idea to list any sub types they have if the party happens to still have that goblinoid bane weapon you handed out 4 games ago.
The Bugbear boldly swings his 'Sparkling Mace of Unicorn Dust' at you with his next attack!
Every bad guy needs attacks and powers, but you don't need to do all the math. You generally know what will hit your PC's and what wont (your rulebook usually provides example challenges and attack curves you can steal stats from as well). Most monsters should always have about a 50% chance of hitting, 75% if they don't do much damage, but also have some sort of hindering effect on the PC's, and about 40% if they deal critical damage or deadly attacks. Attacks that will knock a PC immediately into a death count should only hit about 10% of the time and should always allow for the PC to save or use an extra defense against it.
And When it Comes to Spellcasters!
You don't need their entire spell list, just the highlights will do, and make sure you write out the stats for these. If you have to grab the rule book every time you cast a spell your combat will come to a screeching halt. Its okay to add a few cantrips with one sentence descriptions to this list as well. Use Light, and Detect Magic are a given success unless the PCs interrupt the spell somehow.
Health? Check. Mana? Check.
Your monster's core stats are not their strength, intellect, wisdom, and luck. You don't need these because the likelihood that they will come into play are very low. What you do need are how many hit points they have, what their armor and other defenses are, and any sight or perception bonuses they might have. Everything that has to do with the PC's finding and hitting them and everything it will take for them to hit the PC's back. When setting armor values the PCs should hit the basic monsters 70% of the time, elites 50% of the time and bosses 40% of the time. If you want a monster to last longer or seem tougher give them more hit points instead of lowering the PC's hit percent (you might even increasing the hit chance and double their health). Alternately if you want to simulate a fast or well armored monster give them the lower hit percent but also lower their hit points.
Now What?
by now you should have something that looks like this:
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Orc Bonebreaker Shaman (Oni, humanoid)
Health Points: 30, Mana Points: 15
Heavy Armor +12, Block +10 (or whatever your game uses for defenses)
Perception +10; Low-Light Vision
Speed 6
Battle Axe
Attack +12; Damage 2d8+4
Blinding Hex (3 Mana, Casting Time 3)
Attack +15; Damage: 1d4+2 & Blinded until end of Next Turn.
Jolt (5 Mana, Casting Time 5)
Anytime someone attacks you with a Melee attack they take 5 points of Electricity Damage. This effect lasts 2 rounds.
Other Spells: Light (Casting Time 1), Detect Magic, See Invisibility (Casting Time 2).
Other Skills: Athletics +15, Mental +5, Intimidate +15, Social +5, Spell Save +10
Loot: 30 copper, 1 silver, simple battle axe, ruined leather armor, and 1 hex bag.
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This example was an easy 10-minute monster that could be recycled if you rename the fluff and tweak the stats for your desired party level. Keeping a binder (or file if you prefer computers) full of "prototype" monsters is a great way to always be prepared for a game.
You will notice I also added generalized skills and loot at the bottom. The skill lists are a catch-all if the PC's do something that requires the monster to use something not listed on the sheet. Also, note the loot is not what they will receive every time they kill this monster but a list of optional treasure and the maximum amount of coins you should ever award.
-Adam
