Blue can be obtained from Mew pack in the Mythical Island set
The 2-prize duel in the upper room is absolutely brutal since it actually uses a legit strategy and a pretty decent decklist containing Scyther, Wigglytuff, Mysterious Fossil (+random evos)/Clefairy Doll and at least 3 Bill and Oak from what I recall
Shroud MTG rule states that "this permanent or player can't be the target of spells." This means that any spell that would target the card with defensive power will be unable to do so
Honorable Mention #2 - (#12 Overall) - Greven, Predator Captain $0.75 for this Rakdos five-drop that's in a strong 1,636 decks for you folks (According to EDHREC.com)
Either way, having 20 creatures in play to win is definitely possible, but you should be winning from there with a simple mass-pump effect like Overrun as well
As part of this effort, I requested that they each hide a "Q" somewhere in the art, and they all did