Since Murloc Pally is a passive that keeps getting better, and the shaman quest has a limited upside and basically requires shudderblock to not completely suck, and your minion can get dirty ratted, and only affects played minions. how about a quest along the lines of:
For each different minion type you play after 6, subsequent minions get a random adaptation when summoned. (played if murlocs get nerfed).
Let people make some truly degenerate decks with one of each minion type and get those 1 cost amalgams cycling getting ever more buffs each time.