20 cards where the set is “m21” and the cards are exclusive Planeswalker Deck cards

Adherent of Hope (Core Set 2021 #321)
Basri, Devoted Paladin (Core Set 2021 #320)
Basri's Aegis (Core Set 2021 #322)
Chandra, Flame's Catalyst (Core Set 2021 #332)
Chandra's Firemaw (Core Set 2021 #333)
Garruk, Savage Herald (Core Set 2021 #336)
Garruk's Warsteed (Core Set 2021 #337)
Historian of Zhalfir (Core Set 2021 #325)
Keral Keep Disciples (Core Set 2021 #334)
Liliana, Death Mage (Core Set 2021 #328)
Liliana's Scorn (Core Set 2021 #329)
Liliana's Scrounger (Core Set 2021 #330)
Mystic Skyfish (Core Set 2021 #326)
Predatory Wurm (Core Set 2021 #338)
Sigiled Contender (Core Set 2021 #323)
Spirit of Malevolence (Core Set 2021 #331)
Storm Caller (Core Set 2021 #335)
Teferi's Wavecaster (Core Set 2021 #327)
Teferi, Timeless Voyager (Core Set 2021 #324)
Wildwood Patrol (Core Set 2021 #339)

This search is finished. Now the real work can begin.