Accuracy is a non factor for every extreme but Leviathan. For attacking Leviathan from the front (including spumes) you need 472 to have 100% accuracy or damn near close.

472 is also the magic number for the first coil except Turn 5's adds. You need like 481 for those.

These are physical dps numbers. Casters need 420 instead of 472. Summoner needs a bit more.

For the second coil, physical needs around 500 accuracy to be safe and casters need like 460.