During the Soviet-Polish War, the Soviets diverted soldiers toward the Polish Corridor with the goal of taking it and giving it to Germany, who they theorized would be their ally in a wider revision of the Versailles Treaty.
Perhaps in TTL this is pulled off without somehow provoking a Franco-British attack on Germany--maybe the Germans play up the anti-Communism card to justify occupying it "ahead" of the Soviet troops.
Also in OTL, I think the Soviets had diverted troops in Poland toward Hungary to support the Communists there, although given the timing, they might not have gotten there in time to stop Admiral Horthy from overturning the Reds there.
(Of course, if there were enough of them, they could overthrow Horthy and take revenge.)
Best-case scenario for the Soviets is Red Hungary and a new partition of Poland. The Baltic states can be rolled up later, although the Germans might want a piece of that pie too.
This doesn't lead to a Communist Germany, although the Soviets as allies might weaken domestic German anti-Communism--they'd be more inclined to view the USSR as a friend.
That might lead to Communism being stronger in Germany in TTL and an eventual Communist takeover, or at least the KPD having a role in the government.
Failing that, you could have a *WWII between the USSR and a non-Communist Germany--say the Germans want Anschluss and the Soviets want Constantinople and to spread Communist generally and that means war with France and Britain.
About Japan, with the Soviets being scarier in TTL, maybe the British insist on retaining the Anglo-Japanese alliance. Given the bad blood between Russia and Japan, the West might see Japan as something necessary to contain the USSR and might tolerate their activities to a degree--perhaps Manchuria but not China proper.