This is also taking into consideration cards that are exclusive to Magic: The Gathering Arena, various foiling types, The List, and so many more
Dice-rolling, sideways-prints (Burning Cinder Fury of Crimson Chaos Fire), fused cards (B.F.M
Sliver Queen was the first five-color card, and it made it count
The most obvious use of Genemorph Imago is to target itself and get attacking, which is quite strong already
Interaction density is the percentage of your nonland cards dedicated to answering opponents threats: targeted removal, counterspells, board wipes, and enchantment or artifact destruction
I fondly remember when Shards of Alara first came out and all I wanted was a crispy Elspeth, Knight-Errant from that set