Changeling was introduced in Lorwyn, this is on creatures that are, in the game, have all creature types. But that's inconvenient for printing purposes, so this keyword is used instead.
- 702.70a. Changeling is a characteristic-defining ability. "Changeling" means "This object is every creature type." This ability works everywhere, even outside the game. See rule 405.2.
- 702.70b. Multiple instances of changeling on the same object are redundant.
- 702.70a. - This ability isn't static, it is always happening in all zones, even out of play. It defines the characteristic.
- 702.70b. - Changeling does not stack.