Less than 50 words:
Arcs of amulets form around the boss from center to the border of the field, then twist and scatter into umpteen little walls of bullets that start overlapping after 20 seconds. The attack requires quick reflexes and good pattern reading skill.
More than 50 words, but still one sentence :V :
Arcs of amulets form around the boss from center to the border of the field, then twist and scatter into umpteen little walls of bullets,some of which have tiny gaps, that curve outwards and require fast reaction and a good skill in reading the pattern in which each singular wave of walls dissolve, which becomes extremely difficult after twenty seconds when the waves start to overlap, after which you still have to last more than half a minute as the attack is immune to bombs and takes allot of damage, which, combined with the fitting and generally awesome music of the battle, all in all makes for one of the most difficult, mesmerizing and fun attacks in the whole game series.