The Creeper's from the upgrade pack state "during your turn, if you discard a Keeper you have in play you may move this to another player." Does the Creeper alone allow you to discard a Keeper or do you need another card's effect to discard a Keeper then use the Creeper's effect? And can you get rid of two Creepers with a single discarded Keeper?
It's just "if".
The Creeper doesn't give you an extra ability to discard a Keeper. It just says what to do "if" you discard a Keeper.
Contrast this alternate wording:
During your turn, you can discard a Keeper you have in play to move this to another player.
which is similar to Gold-Pressed Latinum's
You can discard this to steal any Keeper...