Big Noncreatures (Blue/Red) As is Izzet (blue/red) tradition, the archetype is about casting noncreature spells
Those collections just so happen to have some of the most valuable cards available right now a full-art special illustration rare Umbreon EX, nicknamed Sunbreon, and a full-art secret rare Charizard EX
Both sides of the card are viable thanks to the spell denial on your turn, meaning this is one of the few cards that really encourages the transformation aspect of getting it down early for the lower cost, then paying the higher cost to transform it when possible
Unlike Sower of Temptation & co., Agent plays for keeps with an ability that persists even if it leaves the battlefield
Purphoros has ended more games of EDH than 99% of other red cards
Most people tend to focus on the art but there is another element to Magic cards that I feel is too often overlooked: flavor text