If a creature is attacking a planeswalker, the controller of the planeswalker is the defending player
Most life-gain cards seem to be three or lower in cost, and most life-gain decks can easily gain three life a turn
Not only can it phase out some of their creatures, but it might also take out one in combat
Opponents of this card are usually concerned about new, powerful designs homogenizing the Commander format, and Archaeomancers Map is definitely an efficient enough card to be a talking point in that conversation
Very premium product, and classic cards
PuPu UFO looks incredibly mediocre to me, and Im only hedging with the rating because the ability to play a 4-drop on turn 3 is extremely powerful, even when done inefficiently