Mystic Enforcer could easily be slipped into more "normal" builds than its cheaper brethren for several reasons
Either way, he's not looking great
I don't know that I really like Serra as the flying lord
3-mana: +: One 0/1 (Nissa, Voice of Zendikar), one 1/1 with defender (Daretti, Ingenious Iconoclast), one 1/1 with upside (Grist, the Hunger Tide, Modern Horizons) 0: Two 1/1s you sacrifice at end of turn (Chandra, acolyte of flame, not actually protective tokens) -1: One 1/1 with flying (Dovin, Grand Arbiter
I would feel almost entitled to run this in mono white, given the color can still sometimes feel like its punching up, but what makes white decks able to utilize this well is the lifegain that white can do very well
Collector boosters focus on foils and rare treatments, making them more fit for collectors, while set boosters lean toward casual fun with story-driven cards and regular lands for more regular play