how to tell if mtg card is rare 15 most valuable and Magic: The Gathering cards Understanding Card Rarity in MTG:

1 Niv-Mizzet, the Firemind

Its an enchantment in either case, but its only a noncreature spell when cast as an aura

It can only be cast before combat damage is dealt and doubles a creature's power

It also functionally produces mana upon entering, which enables a number of multi-card combos looking to blink this card near-infinite times

In exchange for exiling your tutored cards face up, you get to effectively steal opposing tutors for yourself, and you can spend mana as thought it was mana of any color to cast your stolen cards

You can tell this by looking at how the prices on these variants compare to the standard versions of the card in question