To determine Sunderflock's total cost, start with the mana cost (or an alternative cost if another card's effect allows you to pay one instead), add any cost increases, then apply any cost reductions
Obviously on the vanilla test it is incredible, but the requirement of a creature needing to die is harder to set up than you might think
Many control decks could be crippled or even outright beaten if you caught them with their win condition and catching their only mass removal spell could be devastating as well
If you are looking to collect the rarest cards in Lorcana The First Chapter, you will need to open a lot of booster packs
X cant be 0. Its stupidly powerful, and well mill anyone who disagrees
Caller of the Untamed is probably the best, but I can imagine a home for all five of these in the right Cube