The second factor, rarity, is also multifaceted
Over the years, the base stats have changed on creatures with firebreathing, but none have been at the low point that we saw with Blistering Dieflyn
Ezuri, Renegade Leader saves other elves from destruction while Tyvar, the Pummeler can save itself, and both have a 5-mana mass pump effect
Whenever you cast a noncreature spell, you choose one of the following options that hasn't already been chosen that turn: Solar Beam - The Vision gains Double Strike until the end of the turn Destiny Control - The Vision gains Indestructible Technopathy - Draw a card This is similar to how Monument to Endurance works, a popular artifact from Standard used most commonly in Izzet decks, only it activates with noncreature spells being cast and not discards
You get to play a land each turn, but there are no limits to how many artifacts we can play in a given turn
If Spider-Man sells out across the globe quickly and Wizards of the Coast limits how much they print, then a $100 price tag may be warranted (if the card is as powerful as it seems)