Skull Crushers

Whenever you roll a 5 or 6 on a die, your Brute attacks get +1

this turn.

Whenever you roll a 1 on a die, destroy this.

Battleworn

Rulings

From the Everfest release notes

Both triggered effects on Skull Crushers can trigger more than once per turn. If you have rolled a 5 or a 6 multiple times in a turn, the ability triggers that many times.
The triggered effects both trigger on the result of a roll. If a die is rerolled (i.e. Gambler’s Gloves), only the final value is used; or if it is ignored (i.e. Ready to Roll), any ignored values are not used.
If multiple dice are rolled, the triggered effects are triggered by each die rolled this way (excluding ignored rolls).
The first triggered effect generates a +1 continuous effect that lasts until end of turn. Destroying Skull Crushers does not remove the continuous effects generated this way.
Brute attacks include Brute attack action cards, Brute weapons, Brute Ally activated attacks.
You cannot roll a die unless an effect instructs you to.

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.