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They say it build immunity over time to a single element type sleep. So using Sleep/Sleep II over and over it'll resist. I just believe it's random since we got it slept a few times after it started resisting. If done right you just need to sleep 2-3 times and it won't resist.

Using the SAM method takes a lot of attention to whats going on. They need to know when to WS relative to Freeze cast time.