It seems like the mythic symbol doesnt matter as much for this, the assorted Wizards releases indicate that they all drop at the same rate in this slot
For example, if you've spent three mana on spells so far this turn and you control a permanent with an ability that triggers "whenever you expend 4," that ability will trigger the next time you spend at least one mana to cast a spell this turn
Refer to last picture for the sample of Foil and Non-Foil finishing
Weve had quite a few sets since their introduction, enough that we can rank what things look like on the market for booster boxes
Casting a Chrome Mox, Mox Amber, Mox Opal, or Everflowing Chalice for zero mana and drawing cards can get you major advantage
It was heavily played when it was Standard legal