DeSmuME or MelonDS (MelonDS is widely praised for its accuracy and performance on modern systems).
The Ultimate Guide to Pokémon Parallel Platinum Pre-Alpha Hot
The file was tiny, downloading in seconds. When the game launched, the title screen was silent. The usual upbeat theme was replaced by a low, rhythmic thrumming that made Leo’s desk vibrate. The "New Game" text was a searing, neon pink.