Ravager Wurm

If the target of Ravager Wurm's first mode isn't a legal target as that ability resolves, or if Ravager Wurm has left the battlefield, neither creature will deal or be dealt damage.

Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities are activated abilities and will have colons in their reminder text. An activated mana ability is one that produces mana as it resolves, not one that costs mana to activate.