Recently: https://forum-narutoen.oasgames.com/page/show-post-13079-1.html

- No, all ninjas with prompt mysteries. (saw it on Minato [Jonin], Water main, Sakura [Sailor], Deidara [Edo], Masked Man and Han)

- What's the difference between this and previous point?

- In pvp mostly, like plunder. And very often in arena. Less so in survival and other pve content.

- I guess random. Though all appearances have in common that I'm trying to use Mystery during the round, after certain trigger (like after opponent's healer's standard attack, or after I gain chakra from clones dying) or close the end. In the first case it is usually "just" delayed (which still hurts because I very often miss cooldown reduce for Minato [Jonin] because of it), in the latter it doesn't launch the mystery until next round starts (using newly gained chakra instead of the one from previous).