1. They require psychic. The card is completely clear on this. See Below
2. No
3. Only the first. Block is revealed during the Avoid Attack Step and counts as a defense. Under the Avoid Attack Step it states: "If the attack is avoided, skip to step 5: Additional Strikes"
"Mind Shield may be revealed during the Counter Spell or Avoid Attack Steps to counter a psychic spell or cancel a psychic attack, respectively. If a psychic enchantment is revealed on this creature, you may immediately reveal Mind Shield. Cancel and destroy that enchantment before its reveal costs are paid. Then destroy Mind Shield."
From the text of the card we can glean that it's defensive ability that can apply to spells, attacks, and enchantments but only applies to those that are considered psychic. To determine whether a card or attack counts as psychic you would look for the keyword in the upper right-hand corner or the symbol of an eye on the attack such as the one on a Psylok's attack. Galvitar is described as Force and does not have the eye symbol on either of the listed attacks so it does not count as psychic and cannot be effected by Mind Shield.
