Night Market Lookout

• WWizards of the Coast2016-09-20
  Official Ruling
  This is a triggered ability, not an activated ability. It doesn't allow you to tap Night Market Lookout whenever you want; rather, you need some other way of tapping it, such as by attacking.
• WWizards of the Coast2016-09-20
  Official Ruling
  For the ability to trigger, Night Market Lookout has to actually change from untapped to tapped. If an effect attempts to tap it, but it was already tapped at the time, this ability won't trigger.
• WWizards of the Coast2016-09-20
  Official Ruling
  In a Two-Headed Giant game, Night Market Lookout's ability causes the opposing team to lose a total of 2 life.

Rulings via Scryfall