Q: I play Juvenile Dragon while controlling 2 other Dragons. After the attack has been declared, my opponent destroys one of my other Dragons, and my Juvenile Dragon loses Quickness. What happens to the attack?
A: If the attack has already been declared, the battle continues as normal. If instead, they were to destroy another Dragon before you were able to declare the attack, then you would not be able to attack with Juvenile Dragon unless you played another Dragon and had it gain Quickness once again. (See battle – section 8)