Guiding Ariadne - The main reason why you're still alive, even after activating all that Counter Traps, although we're not really using Counter Traps that pay LP for cost, so the only thing this card will mitigate is the discard cost to maintain card advantage
The former is a big dragon which draws a card and gets larger whenever a permanent it's controller controls is sacrificed
As for the best of the new creatures, O'aka, Traveling Merchant turns your excess counters into carddraw, and Maester Seymour grows creatures of your choice as you grow him
With the online prices varying so drastically, its probably not worth stockpiling Happy Meals just to resell the cards, but finding the holo Pikachu card could turn a $30 to $40 profit and selling any of the others could definitely cover the cost of the Happy Meal
Morningtide , Shadowmoor , and Eventide have the most scarecrows among all Magic sets