MONMUSU

Yes. MONMUSU is free to play on Steam, so there is nothing to buy to start playing.

The minimum requirements for MONMUSU are: Windows Vista, Intel Pentium 4, 2 GB RAM, 3 GB storage. It runs on Windows only. The recommended specs are in the System requirements section.

No. MONMUSU is a single-player game.

Mostly, yes. Valve rates MONMUSU as Playable on the Steam Deck: it runs, but may need some manual setup.

Yes. MONMUSU is the full base game. You need nothing else to play it.