Got Taronyan, Doggynyan and Orgalus already. He's probably worth grinding as a Tough single attacker, right?
Yeah. Though I hear Uber Geeko is better. Still, good to have two Tough Single Attackers.
Since Taronyan and the other three are from Busters/Blasters, that opens up the likelihood of seeing more Yo-kai introduced in that game showing up. We've already had the Score Attack bosses. Usapyon is another major one, along with Fuu2 (Nate's Yo-kai form), Lord Enma, Nuraihyon, Whispocrates (Whisper's original form), Robonyan 3000, Nyanmajo, Nyankishi, Pink Emperor, Onigumo, Onigama, B-Jibanyan (Jibanyan in a Ghostbusters costume), Marshall Burly, Tsuchinoko Seijin, Shimepponia, and probably some others I'm missing.
I also hope Busters/Blasters is being announced at E3.
EDIT: I can confirm that the third Hidden Stage is opened by beating Stage 44 (with Multimutt) with Orgalus' Soultimate. I just remembered that Oracanos was the same. In it you can grind on Lie-In Heart
First Hidden Stage is unlocked by beating Stage 10 with Walkappa's Soultimate
Second Hidden Stage is unlocked by beating Stage 20 with Touphant's Soultimate.
The first stage is a big one, it contains Mynimo. He's normally only available through the Raw Easter Coins or through Medal Battles, where you have to buy real medals and scan them into the game for points, and even then you're not guaranteed Mynimo. So yeah, take this opportunity.