More on the topic of "lag issues" - even your prompt might get the bad treatment if done too late.

Example - you have a chakra generator in pos4 (LM with "Clear mind", Mabui, etc.). They do their generating move and you technically have enough chakra to use another mystery in this round. Well, you literally have a split second to queue it after you get the chakra. Else, for some unknown reason, it gets treated as if you used it in the next round, effectively wasting whatever chakra you just generated and using the chakra cost from the next round. Which means all of a sudden you just used 20 chakra in r2 and your Shisui is very, very sad now :( And you are probably very dead xD

There are 2 "workarounds" for this, both pretty unreliable:

1) Press "Auto" before that chakra generation happens. That way the AI will automatically use the chakra for an available mystery in the correct round. However, it's "Auto", so expect it to be... well, "Auto" xD

2) Literally, spam the hell out of that mystery *on. That way you ensure the correct target, but you run the risk of wasting chakra as described above.

Something similar c*so happen to non-prompt mysteries if you wait too long before activating it. Let's say you have Anbu Kakashi in pos2 and both your pos 1 and pos 2 win initiative. Your pos 1 attacks, their pos 1 attacks, here comes Kakashi, you are sure you pressed that *on before he even moved and... it's a basic attack. And now he just stands there like an idiot with that telegraphed Raikiri charging xD From personal experience, sometimes even when pressing a non-prompt a whole position before it should happen, you can get rekt by the lag. So use them with great caution.

No, absolutely not. As pointed out already, he protects himself from targetted interruptions + it hits like a truck + it has 2 aoe debuffs on it + has the potential to start a combo. It's just not as easy to use as prompt mysteries are.

Trivia: your non-prompt mystery WILL go off at that character's turn even if the character doing it wouldn't be able to do a standard attack (i.e. affected by Blindness).