It’s easy to add an overlay button that hits both at the same time. Much easier than adding it to the core itself.
Nice, never knew that. How can I add overlay buttons? I just know how to change overlays, and that’s it. lol
To add a button to an existing overlay, just make a button icon in png format and drop it into the directory with the others (or, even easier: just reuse an existing one), increment the number of descs for the overlay (e.g., overlay0_descs = 19 would become overlay0_descs = 20), and then copy/paste the lines corresponding to one of the buttons you want to press (A or B) at the end of the list and change the desc numbers to match. Then, where it says “a,0.whatever,0.whatever,radial,0.whatever,0.whatever”, change the ‘a’ to ‘a|b’ (you can look at the dpad diagonals to see how it should look). Change the first 2 numbers to move the button’s centerpoint to a new location (somewhere close, presumably).
Another option is to just modify an existing overlay with more buttons (e.g., SNES overlay) and change the Y button to A|B.
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Thanks man. I went into the cfg for the nes overlay to see how it looks, and your description helps a lot. Greatly appreciate it
Edit: So I could edit the nes.cfg file on windows and just copy it over to my android phone and it would work?
It should work, yeah.
The flat overlays already do that, I think almost all overlays there have a hidden combo button, see Flat gamepad overlays
You’ll have a hidden A+B between A and B butons in gamepads/flat/nes.cfg
Edit: actually it doesn’t have it yet, I’ll add it.
Thank you. I actually managed to add my own thanks to hunterk’s post, but that would be great for others to benefit too, cause it’s a real game changer.
I Love to playing with Retroarch but there are some point that i miss hardly.
my most wanted features for next years:
-native 50 Hz PAL support for all systems (could be switchable over quickmenu, pressing a hotkey combi or perfectly should be set automatic if you start a european/brasilian game).
-C64 Core with Auto-Playlist and easy disk-swap possibility in quickmenu
-Amiga Core with Auto-Playlist, WHDLoad
-better/simplier Support for input-things like Driving Devices, Lightguns, Trackballs and Paddle Controllers
-more features to setup a controller ( Analog Stick Adjustments, Callibration, setting Controllerstyle, Hotkey-Mapping for QuickMenu for each Controller individually)
-better Support for unofficiall Controller Adaptors (f.e.: the most common mayflash adaptors for SNES and N64 Pads are not working correctly and simply no other adapter i tried runs without some issue [thanksfully mostly minor issues])
-better integration of MAME2014/2016 (importing some of the cool quickmenu settings from FinalBurnAlpha can do a nice job in some cases i think)
-little more accurate Dreamcast and Saturn emulation
-DOLPHIN 
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C-Dogs would make for a cool core too. Even better if based on C-Dogs SDL port, which added additional stuff.
A port of Mesen emulator would be great. It’s the most accurate nes/famicom emulator out there.
The dev lists a possible libretro port in the roadmap on the git page 
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I must have been living under a rock. Never heard of Mesen until today. Tried it on my pc and I’m sold!
Libretro port please!
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This thread is not dead, MeowPC98 is almost done and I may do requests again then.
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Hello Is it possible to have all the cores from Android armeabi v7a availeble for android x86 devices? For instance there is only mame 2000 and mame 2003 versions avalible of the mame cores on x86 android devices. There is a lot of capable android devices with x86 processors. including the chromebooks. thanks
I would like to have more Game&Watch games added to the HandHeld Electronic (GW) Windows core. Is it possible to port the Madrigal simulators or any other simulators available online to this core? The existing G&W games in Retroarch are awesome, and I would really love to see this list growing up!
px68k libretro core an X68000 emulator.
Very WIP but usable. tested on linux64/pi3/win64 (with wine).
First create a ‘keropi’ folder in retroarch system directory. put the x68000 bios files in. Then launch emulator with some content (dim|zip|img|d88|88d|hdm|dup|2hd|xdf|hdf) F12 to enter menu.
here is a win64 build http://dl.free.fr/sdPC80koR
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thank you very much for the win build r-type
Hi Can we have Caprice32 for Amstrad CPC games?
Thanks
sure 
since a long time https://github.com/libretro/libretro-cap32
that said it’s not based on the new dev started at https://github.com/ColinPitrat/caprice32