Like most Pokmon cards, the value of Magearna-EX depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (XY Black Star Promos)
1 Kashtira Fenrir A Special Summon For All If any monster holds the crown for best free Special Summon, its Kashtira Fenrir
For those wondering about every Promo in the Genetic Apex set, a complete list of all released has been included below, enabling you to cross-check and work out which ones you are missing and can still try to get through opening promo packs, or others that you may have to trade for once this feature released further down the line
The main reason being if you actually want a discard outlet Jace might only provide one once
Sacrifice after III.) I For each player, exile up to one other target enchantment or creature that player controls until this Saga leaves the battlefield