A Twist of Fate

There's always an interesting little element in adventures which can often serve to counter the simplistic "I succeed/I fail" approach found in many systems. That's an element called "twists". See, not every situation is cut-and-dry success or failure, at least not in the World of Drama. There's always some fun little detail that defies the flow of events. Maybe, even though your shot misses the Big Bad, it manages to strike the Doom Machine ™ behind him, damaging it and delaying his evil plans for world domination. Maybe, even as you strike the fatal blow to the evil spider demon, she jabs you in the wrist with a venemous spike, threatening your very life.

But how to model these little twists of adventure? Well, it gets to be a little challenging in a d20 system, but it's still doable. The trick is to make it something that doesn't happen all that often, yet still often enough to make it a part of the game.

Getting Complicated
The term I'll use for negative Twists is "complications". They generally make things a good deal trickier. Those familiar with the Mouse Guard system will recognize this idea. It's not necessarily a flat penalty, just a further challenge. Sometimes that can be a penalty, but other times it means that the challenge has gained a new aspect. It's now more difficult to complete the task, because of some factor, and here's where creativity comes in. Here's some examples...

Fighting an Enemy: The enemy gains an additional ability. Maybe one of its existing abilities is slightly toned down, to make way for its new ability, which it now exhibits.
Negotiating: Some new information enters the picture, and it's not necessarily good.
Information-Gathering: Things don't start to line up very cleanly, and a new character enters the picture.

A Bit of an Edge
On the flip side of complications? Edges. Any little thing which gives you a tiny bit of an advantage. It's not necessarily a straight bonus, but something which lets you get a new angle on the situation...or maybe a little side benefit that makes things easier down the road.

Stealth: You happen to notice an important detail.
Information Hunting: A new avenue of research unexpectedly opens up to you.
Diplomacy: You find out a helpful little bit of information that informs your continued attempts.

Implementation
So, how do these twists come into play? One easy way of tracking them is by odd and even rolls of the dice. (If you're not using a d20, it's far easier to track.) Of course, when you roll odds or evens, that's a 50% chance there. That's a bit too often for twists to come into play. If, though, you roll odds/evens three times in a row...well, there's only a 1/8 chance of that happening. (12.5% chance, for you math nerds).

So here's how it works. When you roll an odd or an even, you essentially move one step closer to a twist. Once you move three steps in a row towards one direction, you trigger such a twist. What that twist is can vary, but it shouldn't be completely game-changing. Use the suggestions here as a guideline. They should add a fun little bit of flavor to your adventuring, however.