Heirloom of Snake Hide

Cloaked

While this is equipped face-down, at the start of your turn, if you have exactly 1

, you may turn this face-up.

Battleworn

Rulings

From the Part the Mistveil release notes

Heirloom of Snake Hide’s triggered ability generates a triggered effect and is optional. Its owner may choose to generate its triggered effect as long as the card is equipped face-down in the arena at the beginning of its owner’s start phase. If they choose to do so, this card is made public and the triggered layer goes onto the stack.
Heirloom of Snake Hide’s triggered ability triggers and resolves at the beginning of the start phase. During the start phase, neither player receives priority and triggered layers can not be responded to. Whether you have exactly 1 is checked on the resolution of the trigger.

Keyword notes

Cloaked - Equip this face-down.

Cloaked is an ability keyword.
Cloaked is a game rule that changes how permanents are equipped. Cards with Cloaked that are equipped are placed face-down in the appropriate zone.
Unless otherwise stated by the abilities themselves, abilities are not functional and cannot be activated/triggered/used while the equipment is face-down (e.g. Ward).
If any Equipment with the Cloaked keyword remains equipped face-down through the end of the game, opponents in the game/tournament staff/judges at the event may ask its owner to reveal those face-down equipment cards. If asked, owners must turn the equipment face-up to allow the requesting party to validate the equipment card and the equipment zone its equipped to.

All keywords

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.