For the purposes of completing a set, such as for the set collection screen or for certain achievements, you'll similarly only need a single copy of a card from a specific set as you have a playset of cards with that same name
The reason remains the same: this black tutor looks downright absurd in Witherbloom, the Balancer decks
It can tap for mana just like any other land, and in the event that you have seven cards in your hand, you can tap it to draw a card instead
Blade War-Whip: Providing a friend for Amy, Blade War-Whip also provides the important double strike, and its high equip cost matters less with Amy dodging it
Each time you steal a creature, you see an additional card on your next upkeep, which increases your odds of playing more creatures, and so on