I've only figured out bits of it, like how the gallery is tied to the GameSettings.json in your local savedata. The one I have is:
{"serializationData":{"SerializedFormat":0,"SerializedBytes":[],"ReferencedUnityObjects":[],"SerializedBytesString":"","Prefab":{"m_FileID":0,"m_PathID":0},"PrefabModificationsReferencedUnityObjects":[],"PrefabModifications":[],"SerializationNodes":[]},"items":["FawnForest","Ram","Goth","Cinder","CinderFire","MageUnderDesk","SwordRest","OrcArt","DollGuard","MarineGuardBeer","ArcherShot","MerchantFloor","GoblinDefeat","WizardDream","DragonDream","CastleDream","AlchemistFlowers","Thunder","BunnySleep","SpiderVictory","zavier4lexander","GrandSage","Shark","Gorgon","Slime","PrincessSofa","GameOver","BlindJacketKing","QuintusBath","Unicorn","BlackCatFall","Wolf","Ghost","FoxBrush","BunnyForest","BreaSquat","MageBooks","CommanderBattle","WizardLightning","CommanderFall","CommanderEnd","Dragon","DragonCharge","CommanderAttack","LpchanPrincess","Ceryliarectris","LpchanMage1","Ceryliarectris02","joepekar","LpchanAlc","LpchanMage2","LpchanSword","PiruuMi","Purefire","LpchanBC","Gaolukchup","Joepekar2","glasstrinity2","MenaceCreed","HawkHunting","Tahldon","etrius","GlassTrinittyOkeArt","glasstrinity","nashirasauce","soulreaper162","EtriusAlchemist","hawkhuntingprincess","Niseiki","hawkdarkelf","androsm","VoicesOfMelody","hawkbunny","RidethMochi","hawkhuntingGoth","vf02ss","luxarman","Sebrina","justzaz","soulreaprunicorn","S0id3"]}
But since I know nothing about unity I don't really know what the specific triggers are named within the files so I only have the pieces that I unlocked by playing. Hopefully someone else can figure this out from here. So its a start, I guess?