Netplay¶

NX Redux includes Netplay for local wireless multiplayer. When a game supports it, the hint bar in the game list shows Y NETPLAY:

Y NETPLAY hint in the game list

Press Y to host or join over Wi-Fi or a hotspot hosted by one device. There is no IP to type and no persistent toggle to remember to turn off. Save data syncs automatically before the match starts.

Starting a session¶

Both players pick the same game in their game list and press Y.
One player chooses Host Game, the other Join Game.
Both players choose how to connect: Hotspot (hosted by one device) or WiFi (the local network).
The joiner picks the host from the Select Host list. Devices find each other automatically.
Save data syncs, then the match starts.

Supported systems¶

Netplay works only on the cores below. The Y NETPLAY hint appears only for games in these Roms folders. Systems not in the table (Nintendo DS, Virtual Boy, Neo Geo Pocket, the Atari and Commodore machines, and so on) have no netplay.

System	`Roms` folder	Core	Netplay type
Game Boy	`Game Boy (GB)`	gambatte	GB Link — link cable games (Pokémon trades and battles, etc.)
Game Boy Color	`Game Boy Color (GBC)`	gambatte	GB Link — link cable games
Game Boy Advance	`Game Boy Advance (GBA)`	gpSP	GBA Link — wireless adapter and link cable games
Nintendo ES	`Nintendo ES (FC)`	FCEUmm	Lockstep
Famicom Disk System	`Famicom Disk System (FDS)`	FCEUmm	Lockstep
Super Nintendo ES	`Super Nintendo ES (SFC)`	Snes9x	Lockstep
Super Nintendo ES	`Super Nintendo ES (SUPA)`	Mednafen Supafaust	Lockstep
Sega SG-1000	`Sega SG-1000 (SG1000)`	PicoDrive	Lockstep
Sega Master System	`Sega Master System (SMS)`	PicoDrive	Lockstep
Sega Game Gear	`Sega Game Gear (GG)`	PicoDrive	Lockstep
Sega Genesis	`Sega Genesis (MD)`	PicoDrive	Lockstep
Sega CD	`Sega CD (SEGACD)`	PicoDrive	Lockstep
Sega 32X	`Sega 32X (32X)`	PicoDrive	Lockstep
Sega (Genesis Plus GX)	`Sega … (GPGX)` folders	Genesis Plus GX	Lockstep
Sony PlayStation	`Sony PlayStation (PS)`	PCSX-ReARMed	Lockstep
Arcade	`Arcade (FBN)`	FBNeo	Lockstep
Nintendo 64	`Nintendo 64 (N64)`	Mupen64Plus (standalone)	Up to 4 players, device-dependent (details)
Sega Dreamcast	`DreamCast (DC)`	Flycast	GGPO rollback, 2 players (details)

Both players must use the same system folder (and so the same core) for the same game.

Netplay type	What it means
Lockstep	Both devices run the same game and swap controller input every frame. Suits games with a built-in multiplayer mode.
GGPO (Dreamcast)	Rollback netplay. Stays responsive over Wi-Fi.
GB Link / GBA Link	Emulates the link cable (and, for GBA, the wireless adapter). Trading and versus battles in single-player cartridges work between two devices.

Game Boy Advance: use the GBA folder, not MGBA

Only gpSP in Game Boy Advance (GBA) supports netplay. A GBA game in Game Boy Advance (MGBA) (the mGBA core) shows no Y NETPLAY hint and cannot host or join. Move it to Game Boy Advance (GBA) to play over link.

The same applies to Super Game Boy (SGB), which also runs on mGBA. Put Game Boy games in Game Boy (GB) / Game Boy Color (GBC) for link play.

More detail

Lockstep is classic frame-synchronised netplay.
GGPO keeps things responsive because each device runs ahead on its own input and quietly corrects when the other player's input arrives.
NX Redux ships two Game Boy Advance cores in two Roms folders: gpSP in Game Boy Advance (GBA) and mGBA in Game Boy Advance (MGBA).

Different versions of one game¶

You can join a host running a sister version of your game, such as Pokémon FireRed and LeafGreen. The joiner is asked first:

The host is running Pokemon - LeafGreen
You are running Pokemon - FireRed
Join anyway?

Press A to join or B to go back to the host list. On a Hotspot join the same question appears while connecting.

Only confirm when you know the two games link

The wizard cannot tell a sister version from a genuinely different game. A real mismatch fails inside the game, not in the wizard.

More detail

The join step checks that both devices run the same game by comparing the ROM file names. It ignores case, punctuation and anything in brackets, so Pokemon - FireRed (USA).gba pairs with pokemon_firered.gba without any renaming.
Two versions of a game have different names: Pokémon FireRed and LeafGreen, Ruby and Sapphire, Gold and Silver. Those link fine on real hardware, so picking such a host is allowed.
Both devices must run an NX Redux build that includes this prompt. An older host still answers "The host is running a different game." and the join is refused.

Saves¶

A netplay session never overwrites your own save file.

Netplay type	Whose save is used
Lockstep cores and Sega Dreamcast	The host brings the save. Both devices start from the host's progress.
GB Link and GBA Link	Nothing is copied. Each device keeps and plays on its own save.

Give each device its own save

Two Pokémon games with identical saves share a Trainer ID and refuse to trade.

More detail

Lockstep and Dreamcast: at the start the host's save is copied to the joiner. The host plays on its real save as usual. The joiner plays on that copy in a scratch area, and its own save in Saves/ is left exactly as it was.
The copy matters because some of these cores (the Sega and PlayStation ones) keep battery saves outside the shared game state. Without it the two devices could drift out of sync.
On Dreamcast the host's save includes the memory card and console settings, and both devices agree on a BIOS. See Dreamcast → Netplay.
GB Link and GBA Link: link-cable play needs each device to keep its own save.

During a session¶

Save states, fast-forward, rewind and reset are turned off during a session to protect the connection.

Pressing MENU doesn't open the full in-game menu. It asks Leave netplay?:

Button	What it does
`B` Continue	Goes back to the game
`A` Leave	Ends the session and returns you to the game list

On most systems both players pause while the question is open, with no time limit.
After one player leaves a Lockstep game, the other can keep playing on their own.
On Dreamcast the other player's game waits for you. The question counts down and you leave automatically after 20 seconds. The other player sees Netplay ended right away.