Any card cut or damaged in a way that compromises its use as a collectible or for play is considered unacceptable
This is why its a good idea to pair Goofy, Knight for a Day with Tiana, Celebrating Princess another steel card in Rise of the Floodborn as its ability prevents opponents from playing actions if you have no cards in your hand.
Is It Possible to Complete All Secret Missions
Look at this card from Legendary Treasures
#136: Thalara: The Last Artifacts A simple black background isnt a bad choice for a trading card back, but it probably shouldnt be the only choice
You may choose any card type, but the ones that may appear in your library are artifact, creature, enchantment, instant, land, planeswalker, sorcery, and tribal (a card type found on some older cards)