Mistcutter Hydra

• WOTC Official Reminder Textofficial rules
  Protection — This permanent can't be damaged, enchanted, equipped, blocked, or targeted by [quality].

• WWizards of the Coast2013-09-15
  Official Ruling
  Spells that can't be countered can still be chosen as the target of spells or abilities that try to counter them. Although the spell won't be countered, the spell or ability that tries to counter it will resolve, and any other effects of that spell or ability will happen.

Rulings via Scryfall