collector booster box Amazon.com: Magic: The Gathering Modern Horizons 3 from iconic characters to sweeping settings Marvel Super Heroes Collector Booster

(1 monster can only be equipped with 1 Union Monster at a time

I think the main use is to give protection from a removal spell for 2 mana, which I believe is a filler combat trick or mostly a sideboard card

GR Gold Rare Grapha, Dragon Lord of Dark World X DARK Level 8 [ FiendEffect ] ATK 2700 DEF 1800 You can Special Summon this card (from your GY) by returning 1 "Dark World" monster you control to the hand, except "Grapha, Dragon Lord of Dark World"

Lower Text [Your Turn][Once Per Turn] When you play a Digimon with [Four Great Dragons] in its traits or place a [Trial of the Four Great Dragons] in your battle area, 1 of your opponent's Digimon gets -3000 DP for the turn

Necron Dynasties and MTG Flavor You can see all three of those ideas in the cards