Secret Weapon does well in decks which have varied effects on their attacks. For example, one attack that draws cards, one that deals area of effect damage, one that applies debuffs to enemies. That way you can find the attack you need on the turn you need it.
Fetching a specific attack is useful but not really worth buying at full price for most decks. The upgraded version is nice if you can return it from your discard pile.
Draw cards until your Hand is full. Exhaust.
Put a Skill from your Draw Pile into your Hand. Exhaust.
Put an Attack from your Draw Pile into your Hand. Exhaust.
Deal 9 damage. Choose 1 of 3 cards in your Draw Pile to add into your Hand.
Apply 3 Weak and Vulnerable to ALL enemies. Exhaust.
