is enemy creature an opponent?
is enemy planeswalker an opponent?
is enemy creature an opponent?
is enemy planeswalker an opponent?
No. Your opponent is your opponent.
Fluttershy is best pony.
Players who oppose you.
Here's the definition straight from the Comprehensive Rules. You'll note that they leave no ambiguity open as to what "opponent" means:
If opponent ever meant a creature or planeswalker (it doesn't), the rules would specifically tell you so (they don't). Clear enough?102.2. In a two-player game, a player’s opponent is the other player.
102.3. In a multiplayer game between teams, a player’s teammates are the other players on his or her
team, and the player’s opponents are all players not on his or her team.