Mathas forces your opponents to work together if they want that tasty card draw, by picking off the creatures you put targets on
Then she doesn't need to physically move the cards around 1000 times, she just needs to adjust her mana pool to contain an extra 1000 mana
Of course, the most expensive ever was The One Ring which sold for a whopping two million dollars
In addition on ETB we draw cards equal to its power so she can potentially net us many cards
In this case, the coin flip works as a generalized board wipe, which you can counter by simply playing a typal deck that aligns with this cards effect: demons, devils, and imps
Like previously mentioned, we want certain basic effects for our deck like ramp, haste, and card draw, but there are rewards for going in on our +1/+1 counter theme