Does the Watcher ability affect all enemy units count as 'choosing' them for the purpose of triggering 'when chosen by enemy spells or abilities' effects?

Ruling: The Watcher does not choose enemy units. It applies a blanket effect to all enemies, which is mechanically different from choosing.

Nuances:

• Effects that trigger "when chosen by enemy spells or abilities" will trigger from targeted spells and abilities that choose specific units
• They will not trigger from blanket effects like Watcher that affect all units without choosing
• Examples: Would trigger from targeted spells, but not from effects like Unchecked Power or Watcher