There are two vital reasons: to verify the authenticity of a card both for collectors and official play and to ensure you can adequately protect your card with sleeves and binders
Even though this format has a lot of Clues, they arent plentiful enough in all the color pairs for this to be main deck material though
"Introducing Play Boosters: The Best of Two Worlds, Combined"
Ogerpon Box Pokmon: 22 4 Hoothoot SCR 114 4 Noctowl PRE 78 3 Teal Mask Ogerpon ex TWM 25 2 Wellspring Mask Ogerpon ex PRE 27 2 Lillie's Clefairy ex SV9 33 1 Mew ex MEW 151 1 Fezandipiti ex SFA 38 1 Latias ex SSP 76 1 Pikachu ex SSP 57 1 Bloodmoon Ursaluna ex TWM 141 1 Ditto MEW 132 1 Fan Rotom PRE 85 Trainer: 28 4 Crispin PRE 105 2 Boss's Orders PAL 172 1 Iono PAL 185 1 Professor Turo's Scenario PRE 121 1 Professor's Research PAF 87 4 Ultra Ball SVI 196 4 Nest Ball SVI 181 2 Energy Switch SVI 173 2 Night Stretcher SFA 61 1 Earthen Vessel PAR 163 1 Sparkling Crystal PRE 129 1 Rescue Board PRE 126 1 Lillie's Pearl SV9 93 3 Area Zero Underdepths PRE 94 Energy: 10 5 Grass Energy SVE 9 2 Psychic Energy SVE 5 1 Water Energy SVE 3 1 Lightning Energy SVE 4 1 Metal Energy SVE 8 This has been one of the strongest decks in the meta, and it can be teched differently depending on which deck youre targeting

He's also a legendary creature for some reason, and I'm going to assume that Jalum is a member of the M:TG development team and this is a tribute to whoever Jalum is
Like most Pokmon cards, the value of Rapid Strike Style Mustard 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 (Battle Styles)