Not sure on 2d20 mechanic.Sorry, I'm not familiar with those two. Can you expand a bit?
Sounds to me like just a high-fallutin' way of saying "Rule of Cool".Based on something pemerton wrote, I decided to check out Dying Earth. And I really like the Overarching Rule of Efficacious Blandishment.
"The overarching rule of efficacious blandishment states that a character who tries to do something outside the letter of the game’s other rules may do so, provided that the player convinces the GM that this action falls within the spirit of the story. Thus the only true circumscriptions on your actions are maintained by the twin poles of your persuasiveness and your GM’s gullibility."
That works for me. It's sort of the anti-Rules Lawyer provision; don't try and convince me what you think the rule is, convince me that the rule should be broken.
Another genius Robin D Laws idea: insightful, practical and written in a way appropriately for the game.Based on something pemerton wrote, I decided to check out Dying Earth. And I really like the Overarching Rule of Efficacious Blandishment.
Sorry for my ignorance, but was that not the case in other editions of D&D?DM determining when a check is called for. Likely in a ton of game but it's opened up a whole new world for me.
Erm, "single" game mechanics.Many of mine have already been said so rather then repeat I'll move on to the next tier:
Marvel Heroic Roleplay (and presumably other Cortex games) of using your narrative to build your dice pool from separate sets of possibilities, and being able to target/take damage besides just physical.
Another MHR that XP unlocks cool things, not makes you more powerful in your main abilities. You are a competent hero to start. This breaks the mold of advancement of many games.
Blades in the Dark having recovery based on following your vices during downtime. (I guess MHR does this to a limited degree with recovery during transition scenes, but I like the vice-specific focus.)
Don't Rest Your Head dice pools made of different color dice depending on where you are adding it from, and the source of the highest die is very important.
13th Age ... whew, so many good 13th Age points have already been posted, I just want to mention weapon & armor by class and type and skin it how you want. So you there are no sub-optimal weapons/armor and you can describe what fits your concept. For example, all 1H martial weapons do the same damage for a particular character.
Effect first, then skin. Champions (now Hero) was the origin of this for me, with building super powers based on what they do and then adding special effects onto it. It has a whole bunch of classic types of powers stripped of special effects, such as Energy Blast instead of Laser Beams, Fire Burst, Ice Needles, Rockets, etc. You have advantages and disadvantages you can add on. That's it for the math. Skinning it is next. So you can cover a huge amount of super powers (or magic, or advance tech, or ...) with a base selection.
Recovery based on roleplay. I think I first saw this back in the early 90s with World of Darkness. Everyone had a exterior face and private face picked from a list, and you recovered based on RP that matched either of them. This concept doesn't have to be just recovery, Fate compels are a similar concept and that's to get plot currency.
Some of mine are already mentioned so I'll get those out of the way (heh):What are yours?
Love, love, love how this got rid of all those piddly modifiers. I know other games have done similar things, but this was my first massive exposure to the mechanic.D&D's advantage/disadvantage is a really elegant way to replace all those fiddly bonuses. It's one of my favourite things about 5E.
I really like this one as it give each round something new and interesting.Stunt Points (Dragon Age, Fantasy Age): roll 3d6, doubles on rolls generate Stunt points equal to the value of the off-colored stunt die that a player can spend on various cool things
I also like "fortune" in The Expanse.
These two are quite similar in outcome and I really like it. As I've mentioned elsewhere many times, I am a huge fan of Savage Worlds, but the "death spiral" can be a bit trying at times. So much so that I've just stopped playing it for other games that don't have that. I like the "unrealistic" feel of watching the points drop until the character drops while maintaining the effectiveness of the character until that pivotal moment. I didn't think I did, until I left SW to return to D&D5e. It was at that moment that I realized just what I didn't completely like about SW (I still love SW!)I really like Hit Points as a simple, abstract measurement of health.
There are certainly ways to adjust these things though, if "hitting" becomes too easy. I believe that the Fantasy AGE Companion provides some alternate rules (especially to address the oft-cited problem of HP bloat) and there is the upcoming Fantasy AGE Campaign Builder.I really like this one as it give each round something new and interesting.
One of the chief complaints I hear about the AGE system is that "hitting" the target becomes ridiculously easy as the characters advance in level. My own players, when I was learning the system a while back, really complained about it. But the 3d6 roll really isn't so much a "To Hit" Roll as it is a "Generate Stunt Points" Roll. Once we overcame that hurdle, the game really clicked for us and took off like a shot. (Unfortunately, the campaign and group died because of everyone's Real Life intruding.)