Think of all the extra basic lands, the extra Seize the Spoils copies you pulled from Secrets of Strixhaven , the Goldvein Picks from Foundations , or the many commons, uncommons, rares, and mythics that dont see as much gameplay as the staples in various formats
There are also three colourless cards, one of them being a land.
Also, The Blissey V deck requires the maximum number of Energy Cards to be attached to Blissey, hence, Energy-finder Item Cards are beneficial
Additional components such as a playmat, counters, rule booklet, and promo card
I could easily be wrong, but my early intuition says Tamiyo, Field Researcher is not going to be great
You can use Gallant to either add any Rock monster to your hand or Special Summon a Rock monster from your hand in face-down Defense Position at the cost of detaching one XYZ material