It doesn't have to be the same player, planeswalker, or battle that Arthur or any other attacking creatures are attacking
Anyway, here are some ways Wizards can (and should) fix the FNM promo problem
Beseech the Mirror - $29.38 We see the bargain mechanic again here for our number 5 card - This time on a tutor that can cast your spell for free, assuming it's four mana value or less and you paid the bargain cost
All 12 Pokmon types (Fire, Water, Lightning, Grass, Fighting, Dragon, Psychic, Darkness, Fairy, Colorless, Dual type, Metal), three evolution stages (Basic / Stage 1 / Stage 2) in both holo and non-holo per type, 12 energy dividers (including Special and Foiled), and 4 trainer card types (Stadiums, Supporters, Tools, Items) each in holo and non-holo
So I decided to write an extension for Prism.js to add syntax highlight for these deck lists
She can also win the game in short order, being a combo piece in the command zone