Activated abilities of creatures your opponents control can't be activated.
6/8/2016 Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keywords are activated abilities and will have colons in their reminder text.
3/14/2017 No abilities of creatures your opponents control can be activated, including mana abilities.
3/14/2017 Linvala’s last ability affects only creatures on the battlefield. Activated abilities that work in other zones (such as bloodrush or unearth) can still be activated. Triggered abilities (starting with “when,” “whenever,” or “at”) are unaffected.