Threshold isn't technically a two-in-one mechanic, but it was an important step in realizing the value of cards that represented two distinct concepts
Unlike some of the other options on this list, he doesn't have an additional ability, but not every card needs one to be a solid option
the mana value and name of the original card have to be visible, easy to read, and unaltered
While Wizards owns a lot of the IP on Magic cards (the art, mana symbols, etc.) there is t nothing illegal about a piece of cardboard the same size of a Magic card with some unique custom art that might look a bit like a Mox, an Underground Sea, or a Wheel of Fortune
Later versions of Baby Pokmon cards instead made them Basic Pokmon cards with a Baby Evolution ability, allowing them to evolve while removing damage
Baltoy's presence in Generation III also ties it closely to the advancements in game mechanics introduced during this era, such as the Double Battle format and the more intricate weather systems