Here is the breakdown of the official changes introduced in Version 2.2.0 and its immediate predecessors:

The biggest win for nostalgia. Using the new system (unlocked via the Time Travel mechanic), you can summon 88 classic Yo-kai from the first three games that were previously locked to the ++ expansion. Jibanyan finally has his Charming tribe mates back, including Roughraff and Manjimutt (who is somehow even more tragic in 3D).