Breaking Scales

Attack Reaction - Destroy this: Target attack action card with combo gets +1

.

Battleworn

Rulings

From the Welcome to Rathe release notes

Breaking Scales can only target a card with combo.
The card must have the keyword combo (displayed on a card as Combo – [text]) This does not include cards that just reference combo or have combo in the text box.

Keyword notes

Battleworn - Equipment that wear down after each time they are used to defend. If you defend with a card with Battleworn, put a -1{d} counter on it when the combat chain closes.

When you defend with a card it remains on the combat chain until the chain closes, therefore you cannot defend with an equipment multiple times on the same combat chain.
A -1 counter stays on the card until the card is destroyed or the game ends.
If the defense of a card that is defending is below zero, its defense value is considered to be zero.
When this card is destroyed, it is sent to your graveyard. (Not when it has 0)
When this card is destroyed, it is sent to your graveyard.
If the defense of a card that is defending is below zero, calculate as if its defense is zero.