The fundamental structure of the deck never changes, but rather cards get swapped out as more efficient cards or more cards of the subset required become available
In the case of nonland cards you typically get cards that tap for less mana than you spent to cast them, or that you can't use right away thanks to summoning sickness
Thematic inspirations seem to vary wildly, but it is quite interesting that these specific twenty were chosen among the 63
Acornelia, Fashionable Filcher Camellia, the Seedmiser Chatterfang, Squirrel General Hazel of the Rootbloom The Odd Acorn Gang The Unbeatable Squirrel Girl Tippy-Toe, Terrific Partner Toski, Bearer of Secrets
Two Legends [OP-08] brought a pair of major additions to this decks war chest: Jack and Whos-Who
Perhaps best of all - a fun sticker sheet featuring First Partner Pokmon friends