Gear Dragon Pup

Trample, Haste
As an additional cost to cast, discard 5 cards from your hand. You may not play this if you have less than 5 cards in your hand.
When Gear Dragon Pup enters the battlefield, destroy a total of X non-artifact creatures, enchantments, and/or planeswalkers.
My masterpiece is finally complete. I have finally made a giant dragon and dog hybrid made only of metal. Wait. It is running towards me! Send help! PLEASE!