In 2023 Magic, we see cards that not only allow them to stay, but facilitate the production of these facsimiles
If a transforming card is in your hand, library, exile, graveyard, Command zone, or anywhere else, it's only seen as having the properties listed on the front face
Search the actual rules text of cards to find specific abilities: "draw a card" find every cantrip and card draw spell "destroy target creature" removal options "enters the battlefield" ETB triggers for blink decks "whenever a creature dies" aristocrats payoffs "search your library" tutors "each opponent" multiplayer-focused effects for Commander Combine text search with color and type filters to find exactly what your deck needs
Have a few ways to mass-mill your library, such as Hermit Druid or many of the cards in Innistrad block
Finally, the big daddy product is the Illumineer's Trove, which includes one storage box, two deck boxes, eight booster packs, fifteen game tokens, and one player's guide.