Hello,
This is a known issue with ETR Madara caused by him attacking too many targets. The devs are working on a definitive fix but it has not yet been released. There are workarounds, however. If you minimize the screen or use the Boss Key to remove the screen when the attack happens, it greatly reduces the chance you will crash. Using a different ninja will avoid this bug entirely. Updating to the newest miniclient shows much more stability in avoiding this crash. And finally, using the non splash mystery should avoid most crashes.
Hopefully this gets fixed soon, sorry about the trouble!