Generation 2
GBC-to-GBC Infrared
mGBA doesn't support Infrared. GBE+ does support it, but the performance is very poor, making it pratically unusable.
Infrared is required to obtain all decorations on the same savefile via Mystery Gift.
Check support progress: mGBA GitHub
Workaround:
Using Mystery Gift Simulator from PkCompletionist.
Pokémon Pikachu 2 GS Emulator
There are no emulators for Pokémon Pikachu 2 GS. In fact, the ROM has never been dumped.
All items given by Pokémon Pikachu 2 GS can be obtained elsewhere.
Generation 3
GBA Wireless Adapters
Since 2024-01-13, GBA Wireless Adapters is fully supported on gpSP emulator.
mGBA doesn't support it.
Generation 4
DS-Wii Connectivity
The emulators melonDS (DS) and Dolphin (Wii) can't communicate.
Unable to transfer Mew and Phione from My Pokemon Ranch (Wii) to Diamond/Pearl/Platinum (DS). It is the only non-discontinued method to obtain Mew. Note: Phione can be obtained by breeding Manaphy obtained from Pokémon Ranger US.
Check limitation status: Dolphin Forum
Workaround:
Simulator Tool that transfers Pokemons and items by reading and modifying savefiles.
Check workaround status on PkCompletionist GitHub
DS-PokeWalker Connectivity
The emulators melonDS (DS) and Powar (PokeWalker) can't communicate. It is not possible to use routes unlocked by events.
All items given by PokeWalker can be obtained elsewhere.
Check limitation status: Powar Github
Workaround:
Simulator Tool that transfers Pokemons and items by reading and modifying savefiles.
Check workaround status on PkCompletionist GitHub