If your deck is built incorrectly, then Delver is just a 1/1, and Grim Flayer is similar
Theres a slight difference between modal cards and modal spells
Individual bending abilities like Waterbend, Earthbend, Firebend, and Airbend can work outside the set, sure but Avatar Aang himself becomes much harder to build around effectively, especially if your goal is flipping him consistently
Cyclopean Tomb, Word of Command, Lich, Two-Headed Giant of Foriys, Blaze of Glory, Raging River, Natural Selection, Singing Tree, and Khabal Ghoul, are all on the reserved list but lost value, or did not keep up with inflation, over the past 25 years
For one mana you counter a noncreature spell, which is pretty darn good
Premium production quality throughout