This train shit is so retarded it'd be rejected by Bollywood for being too unrealistic.
Ok so:
1. How do you expect they'd get many thousands of troops onto trains without intelligence assets knowing? Or even just the public? Why wouldn't Europe just block the track?
2. Ok say the magic train does make it to Paris, Berlin, etc. How effective do you think unsupported infantry will be?
3. How will they survive for even a day? And I don't mean raiding an Aldi I mean they will immediately be surrounded by incredibly pissed off local forces on their home turf with a hostile civilian population undermining the operation?
4. How does Russia survive having the entirity of NATO declare war?
1) Kind of easily, since by the time anybody notices that they are being subtly invaded, they wouldn't be able to actually respond. They would need to completely mobilise. You know, how it took Israel like a week to finally stop Hamas from killing its civilians, despite having a fucking wall?
2) Magic train makes it to Paris without being noticed. The soldiers disembark, and the local police are... unable to arrest them. They simply pull off an "Operation Kitona" style takeover - they seize control of the main station and overrun the local police and authorities. The local authorities, fearing their own execution, tell the incoming soldiers to "stand down" and negotiate their own release. Russia uses this negotiation time to move more assets into the country.
3) Well so long as the Russians are well behaved, and "immediately surrounded by incredibly pissed off local forces" - the German Bundeswehr wakes up, eager to fight, and bring their broomsticks to the front line. They find... the experienced Russians heavily entrenched, thousands of German civilians as collateral and now have to try to negotiate for it. Confused onlookers film it for TikTok. The local soldiers aren't going to shoot through their own civilians when they're not even sure if the Russians are there as invaders, or if it's some political stunt that they are witnessing.
4) The Germans (France is actually capable of defending itself outside of NATO) quietly surrender to the Russians, since they are now stuck between losing thousands of civilians and facing World War Three on their home turf, or saving face and trying to act like a big military power.
The thing is, three months ago, if I had said "Hamas might launch an assault on Israeli civilians by scaling the wall in paragliders, or using explosives and JCBs to destroy parts of it and flooding in, causing havoc while the IDF tries to stop them!" you would have been posting it on my profile too!
Magic train is just a stand-in for any kind of "way around the defenses for a relatively small portion of the many, many soldiers now positioned almost directly at the EU's border" - we would not have any way of actually dealing with it outside of diplomatically begging for mercy.