I have done two international to international MPM transits, and both times, I've just gone to immigration desk, explained I am going international to international, and they ask you to wait at the seats near the Medical Check Post prior to immigration. Then someone takes you upstairs to departures level. In both cases, I had already checked and didn't have luggage to check onwards with QR, but I got the impression that they would have walked me round to check in desks and then up to departures level.

On one occasion I had luggage to collect from after immigration, to take with me onboard with QR, and it wasn't an issue. They let me walk through immigration to retrieve the bags and then bring them back pre-immigration.

If you're lucky enough to have HLO and are at the right place, they have an elevator as you get off the aerobridges (just before the escalator down to immigration) that takes you to a security desk and makes international transits really easy, but it's not always open so you have to head down to immigration.

They don't ask you for visas or money for visa on arrival.