Rarity

that specific serra angel comes from a sepeciality set

>>54924943
so she is just mythic because the set is specific serra angel?

so not always rarity mean power, just... well... rarity...

>>54924915

This is from a "from the vault" pack, which contain a bunch of foil cards that are, for one reason or another, important to magic's history. They contain cards that were any rarity, but they print them as mythics, because they are basically promos.

>>54925016
From the Vault has been exclusively mythics since the second set in 2009.

>>54925016
That specific Serra Angel is from the From the Vault: Angels which is just a bunch of select cards with new art, foiled out, and all mythic.

If Serra Angel was to be put into a pack in a future set she would be uncommon again probably because the mindset behind rare cards in the current R&D is complexity. Complex cards are rare and tend to have powerful effects. Vanilla creatures that have trample or flying and vigilance as their only abilities will be uncommon and common. Serra Angel falls into that vanilla easy to understand area.