Can the Mask of Avacyn be targeted by spells after it's been equipped to a creature?
This is an odd question, because the mask gives the equipped creature a +1/+2 and has hexproof and says it "can't be the target of spells or abilities your opponent controls", where "it" refers to the equipped creature. However, can your opponent use a spell or ability to directly destroy the Mask of Avacyn (in this case an Artifact - Equipment card)?
Example: Mask of Avacyn is attached to a creature. Can my opponent use the Planeswalker ability of Nicol Bolas that reads: "Destroy target noncreature permanent"?
Alternatively, can my opponent use a spell card that reads, "Destroy target permanent" or Recoil, an Instant that reads:, "Return target permanent to its owner's hand. Then that player discards a card"?