Like most Magic: The Gathering cards, the value of Unstable Mutation depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Ultimate Masters)
If you have enough Rat tokens on the battlefield and a board wipe happens, it's possible that Mirkwood Bats can burn all of your opponents out of the game
Palafin ex 151/131 Special Illustration Rare The first Prismatic Evolutions card revealed in English is also among its most rare, and that is the special illustration rare version of Palafin ex
If you cannot consistently play lands and develop, fix mana before anything else
Blue and white center on going over your opponents heads with flying creatures, while mono green (my favorite and the best way to play) favors big, stompy creatures that run over your opponents defenses