2020-04-17 : If X is 0, the 0/0 Hydra token will die immediately after the ability's done resolving unless something else is raising its toughness.

2020-04-17 : If an effect, such as that of Parallel Lives, causes Zaxara's ability to create multiple Hydra tokens, they each receive X +1/+1 counters.

2020-04-17 : If the spell you cast has {X}{X} in its mana cost, the token gets only X counters, not twice X.

2020-04-17 : The Hydra token enters the battlefield as a 0/0 creature. Any abilities that modify or trigger on this event apply. After the token is on the battlefield but before any player can take actions, +1/+1 counters are put onto the token.

2020-04-17 : The value of X in Zaxara's last ability is the value of X of the spell you cast.