MARCH OF SWIRLING MIST I originally considered Propaganda for this slot on the list
It was the first set to feature a Secret Rare card, the first to include holofoil treatments for Trainer and Energy cards, and the first to explicitly expand the lore of the cards beyond the scope of the original Game Boy titles
"Magic: The Gathering Fact Sheet" (PDF)
As card #187 in a set with 132 printed cards, it sits in the secret-rare numbering pulled less often than anything in the regular checklist
Giant Adephage makes 7/7s with trample, Omnath, Locus of Rage makes 5/5s that will deal extra damage when they die, and Crested Sunmare makes 5/5s just for gaining life
They're not unknown to make some good use of +1/+1 counters, which is where Kalonian Hydra gets into the fun zone