Whenever a nontoken creature enters the battlefield, its controller creates a token that's a copy of that creature.
Whenever a nontoken creature leaves the battlefield, exile all tokens with the same name as that creature.
When Dual Nature leaves the battlefield, exile all tokens created with Dual Nature.
10/4/2004 If Dual Nature leaves the battlefield between when it triggers and when a token is put onto the battlefield, that token remains on the battlefield indefinitely. It missed the separate ability which would have exiled the token.
10/4/2004 If the original creature has any “enters the battlefield” abilities, the copy will also have those.
10/1/2009 The token is not considered to have been kicked, even if the creature it’s a copy of was kicked.
7/1/2013 If a legendary creature enters the battlefield, the token is put onto the battlefield and then the “legend rule” forces its controller to put either the original or the token into its owner’s graveyard before any player can take any actions.