League of Legends Champion Mastery Level 6 and 7 Crests - A How-To Guide

Got stumped with the blue essence bit until my spouse chided me that I can get a random mastery shard by buying a mystery champion shard. I forgot; signs of aging I guess. :D

That solved things. I hope this proves useful. (The main mastery crest thread is six months old; won't necro that.)