Helm of Sharp Eye

Attack Reaction -

, destroy this: Banish the top card of your deck. You may play it this combat chain. Activate this only if you control a weapon attack with

greater than twice its base.

Battleworn

Rulings

From the Everfest release notes

Base power is determined by the printed value on a card. (Located at the bottom left corner of a card.)
Helm of Sharp Eye’s activated ability is an attack reaction. You may only activate it during the reaction window when you are the attacking hero.
You can only activate this ability if a weapon you control has MORE than twice its base power. E.g If you can control a Dawnblade (that has a base power of 3) then in the reaction window play and resolve Razor Reflex, you are still unable to active Helm of Sharp Eye’s ability as Dawnblade currently only has a total power of 6. However, increasing the power to 2 Razor Reflex’s (total power of 9) will allow you to to active Helm of Sharp Eye’s ability.
Non-attack actions can only be played on an empty stack when the combat chain is closed. You cannot play non-attack actions with Helm of Sharp Eye, unless they can specifically be played as an instant.
If the base power of a weapon is 0, any increase is considered greater than twice its base power.

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.