basically Amon Ra has a sub skill AI that summons 2 Kalz when it takes ranged damage when there are no enemies, so a Sin/SinX cloaks and grimtooths Amon Ra and repeats till he has a massive mob.
Also can be done with a party and Ice wall. Constant pressure on the icewall and build a permenent barrier to be released when there are hundreds of kalz at once.