Havoc Wrap

Action -

: Go again

If this is tapped, cards cost

less to play, this doesn't untap during the end phase, and this gets "At the start of your turn, destroy this."

Battleworn

Rulings

From the Compendium of Rathe release notes

Havoc Wrap’s second ability generates several continuous effects if it is tapped. If it is tapped, cards cost less to play for each hero; Havoc Wrap will not untap during the end phase; and it will get a triggered ability that triggers at the start of your turn. When this triggered effect resolves, you will destroy it.
Neither player receives priority during the start phase of a turn.
Effects that increase resource costs are applied before effects that decrease resource costs.

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.