What's strange to me is that this year the only thing they're holding back for future waves is Dark creation crystals. Otherwise, there are senseis of all the battle classes (if you count Chompy Mage, with Flarewolf coming soon) and elements already available, and the same goes for creation crystals (with a limit on the number of Fire crystals at the moment). Usually the release schedules have been a bit more coy than that, I guess in an attempt to reinvigorate interest with each successive wave.
Yes, Wave 3's release next month will bring us to the point where anyone can reasonably pick up anything they want for the game, excluding specific Sensei characters or Crystal molds...
But here are the things you can't readily go to the store and buy now, that one could be assumed to "need" to complete the content inherent to the game: