This is basically the same as the Hellbent mechanic from MtG. A Last Resort condition will take effect for one-time use cards if it is the last card in your hand. Cards in play may also provide a bonus condition when you have no cards in hand.

The mechanic is almost paradoxical in giving you card advantage because to take advantage of it, you're basically playing one and a half card, for every card that has Last Resort; but to do so, you must have very little cards. Players will likely accuse you of having extremely good luck for top-decking(playing cards as you draw them because you have no card) all the time; however, this mechanic is just my integral design of the Rogue class as they don't have traditional card drawing for card advantage. Rogue cards are also intentionally low cost to leverage Last Resort.

Thanks for reading my borrowed-idea-but-obviously-renamed-to-avoid-copyright-issues suggestion on a new mechanic. Looking forward to seeing any comments, suggestions, or flames you have in mind.

Examples:
Note, visit the Decoy mechanics page for more info on it.

Quote Originally Posted by AnAdolt View Post
Name: Infiltration
Card Type: Rogue Ability
Casting Cost: 2
Effect: Deal 2 damage to target enemy. Reduce cost by 1 if Decoy was used this turn. Last Resort—reduce cost by 1.
Flavour Text: "Ma-xi-mum se-cur-i-ty? What's that?"
Quote Originally Posted by AnAdolt View Post
Name: Sulfuric Venom
Card Type: Rogue Item
Casting Cost: 1
Effect: 1 Resource: Target weapon gains 1 attack until end of turn. Last Resort—applied weapon gains 2 attack instead, as long as you have no cards in hand.
Flavour Text: A sharp blade's of no use in the hands of a dead man.
Quote Originally Posted by AnAdolt View Post
Name: The Mastermind
Card Type: Rogue Ally
Casting Cost: 4
Stats: 2/4
Effect: Decoy Master. Last Resort—The Mastermind gets +1/+1 as long as you have no cards in hand.
Flavour Text: He also goes by two other names: cloak and daggers.
Quote Originally Posted by AnAdolt View Post
Name: Stratagem
Card Type: Rogue Ability
Casting Cost: 1
Effect: Target ally gains Escape Decoy until your next turn. Last Resort—gain Escape Decoy permanently instead.
Flavour Text: Let shadow be your home. Until opportunity knocks on your door.
Quote Originally Posted by AnAdolt View Post
Name: Killer Instincts
Card Type: Rogue Ability
Casting Cost: 3
Effect: Kill opponent ally with cost 3 or less. Last Resort—kill opponent ally with cost 5 or less instead.
Flavour Text: Any place, any opponent, any time!