Anyone now this?

Oh yeah, found it:

Search for Re-remastered and click that result, by innociv.
Click Subscribe
Steam will download the mod (<500mb)
Next, launch the launcher and at the bottom right, under Multiplayer, there is a MODS button. Click that, and there you can activate the mod (should appear in the right column).
Then you can launch the game.

If it doesn't show up, Steam may not have downloaded it yet.

You can play it online so long as everyone has the mod. They'll get an error if they try to join with out.
To play it in MP you need to add -mpbeta to Properties -> Set Launch Options in steam.