Advantage & Disadvantage in D&D 5E (and the bizarre creature that foreshadowed it)
If you’ve played Dungeons & Dragons 5th Edition, you already know the rhythm of advantage/disadvantage. The mechanic is simple, elegant, and defines the feel of 5E: roll two d20s, take the higher (advantage) or lower (disadvantage). Possibly one of the most elegant mechanics that 5E introduced, fostering the element of intuitive, quick, and impactful rules for a historically clunky system. But buried in the archives of AD&D lies a strange, almost mythic precursor to this system: an obscure creature known as the Tween.
Decades before 5E cleaned things up, Advanced Dungeons & Dragons was no stranger to experimentation. In 1981, TSR published the Fiend Folio, and in that wonderful book, the Tween was introduced. It was a deeply weird, reality-warping creature that my DM was kind enough to curse my fighter with. I tried porting that creature/curse into 5E and… you probably know where this is going.
How Advantage & Disadvantage Work (and Why It’s So Clean)
5E’s design philosophy trimmed the fat off earlier editions. Instead of stacking tons of situational bonuses, it gives you a cleaner question: Do you have advantage, disadvantage, or neither?
Advantage/Disadvantage Rules:
- Advantage → roll 2d20, take the higher
- Disadvantage → roll 2d20, take the lower
- One of each? → they cancel out, and the player rolls normally
The last rule is critical. It keeps the system from spiraling into chaos.
Under the hood, advantage is strong—roughly a +5 modifier depending on the target number—but it’s carefully controlled. It doesn’t stack or spiral. It behaves itself.
But the Tween does not.
The Tween (Fiend Folio, 1981): A Living Distortion Field
The Tween first appeared in the original Fiend Folio, one of TSR’s strangest monster collections (and my favorite). It’s not just a creature: it’s a problem. A Tween attaches itself to a host and warps probability around them. Not in clean, modern terms, but in effect:
- The host becomes extraordinarily lucky
- Everyone nearby (friend or foe) becomes extraordinarily unlucky
It’s not advantage/disdavantage in name… but in spirit? All day long. It’s close enough to feel like an early, untamed version of the idea. Instead of a tidy mechanic, it was a walking aura of imbalance. That said, the Tween fits naturally into darker campaigns.
When You Try to Bring the Tween into 5e
I tried it. I really did. My DM cursed one of my characters with one in AD&D, so years later, I thought:
Hey—this advantage/disadvantage stuff feels like a Tween, and should port cleanly.
It did not.
What actually happened:
- My player’s character effectively had permanent advantage
- His allies within range had a permanent disadvantage
- The normal “they cancel out” rule stopped working in any meaningful way
- Situational mechanics—lighting, cover, spells—got murky, or outright irrelevant
And the worst part? We had to slow the action to mitigate and interpret rules. It was particularly a nuisance before the players realized that one of their characters had been cursed. “Why are the rules suddenly broken?!” To be fair, the game didn’t break immediately. It just eroded.
Why the Tween Breaks 5E (At a Fundamental Level)
This isn’t just “a little overpowered.” It’s structurally incompatible.
1. It Creates Permanent Advantage
5E assumes advantage is temporary and earned. Make it constant, and suddenly attack rolls spike, crit rates climb, skill checks become trivial, and monsters stop functioning as designed. You’re not playing 5E anymore. You’re playing Watch this character succeed!
2. It Destroys the Cancellation Rule
5E relies on this core idea: One source of advantage + one source of disadvantage = normal roll. The Tween ignores that. When that rule collapses, so do other key aspects of the game like stealth vs. perception, dodge actions, conditions like blinded or poisoned, spells like faerie fire or guiding bolt, and class features like Reckless Attack. We weren’t just bending the system. We were unraveling it.
3. It Punishes the Party
This is the real killer. The Tween doesn’t just empower one character. It also actively drags everyone else down. That was the point in AD&D. It was absolutely a curse. A character with a Tween might as well go solo. And in that regard, it could also be a blessing for those without a lot of opportunities to gather enough friends. A DM could run a solo adventure without nerfing the monsters too much or lying about their own rolls behind the screen.
But in 5E it was different. Your rogue? No advantage on Sneak Attacks. Your paladin? No clean smite windows. Your cleric? Good luck landing clutch spells. It turns one player into the main character, and everyone else at the table resents being background noise.
That’s not imbalance. It’s a table-killer. This doesn’t just bend the rules; it creates situations that feel like metagaming, even when no one intends it.
Could You Use the Tween in 5E?
Perhaps. But not as written. If you love the idea of the Tween—and you should, because it’s cool as hell—you can still use it. Just tweak it. Perhaps use one of the following options:
Option 1: Narrative Curse Only
The character is “unnaturally lucky,” but it’s purely descriptive. No mechanics, arguments, or broken math.
Option 2: Limited Trigger Effect
Once per long rest, the player can gain advantage on a roll, and a nearby ally suffers disadvantage on their next roll. Same flavor, contained impact.
Option 3: Cursed Trade-Off Mechanic
The Tween’s Mark (Cursed Effect)
- When you gain advantage, choose a creature within 30 ft
- That creature has disadvantage on its next roll
Now it’s a decision. An interesting one that’s playable.
Final Thoughts: From Chaos to Elegance
The Tween is a relic from a time when D&D was less concerned with balance and more concerned with possibility. It’s messy, unfair, and fascinating. Somewhere in that chaos, you can see the early spark of what would eventually become one of 5E’s best mechanics. Advantage and disadvantage didn’t come from nowhere. They were refined from ideas like this. Strange, lopsided, experimental concepts that needed time to become something elegant. The Tween is what happens before elegance. If you try to drag it forward unchanged, it will remind you exactly why 5E cleaned things up.
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