Xathrid Gorgon

Text:

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
, : Put a petrification counter on target creature. It gains defender and becomes a colorless artifact in addition to its other types. Its activated abilities can't be activated. (A creature with defender can't attack.)

Rulings:

• 7/1/2012 The effects of Xathrid Gorgon’s ability don’t depend on the petrification counter. If that counter is removed, the creature remains a colorless artifact with defender, and so on.
• 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.