Decoy is a simple trap card that costs a single blue energy. If it is on your bench at the start of your turn, it springs and allows you to draw an additional card that turn. As such, it is a slow deck thinner (It takes a turn to replace itself). If you are out of playable cards and want some further consistency, you can do worse than this, but most of the time there are more effective cards than this to help your deck. It is a nice bonus to use with Giant Shark to reduce its cost by an energy the next turn, though.

Strong against: Destroyer of Dreams (it cancels out Destroyer's hand-emptying ability)

Weak against: Interfere, milling (you'd be helping your opponent mill you)