Armor
Armor items grant benefits while their owner is being The fallback content to display on prerendering. Each has a standard ability that is resolved when an The fallback content to display on prerendering engages an The fallback content to display on prerendering. However, each
also has a secondary, The fallback content to display on prerendering keyword ability that can be triggered during this engage in addition to the item's standard ability. An adventurer must choose whether to use an
ability, including its overtax ability, before damage is dealt. Each
item's The fallback content to display on prerendering is the body area it is worn on; an adventurer can have only 1
with each The fallback content to display on prerendering in their ready slots.
Is there a limit to how many times it can be used in a round?
Armor can be used each time an enemy The fallback content to display on prerendering you (meaning it targets you). If you are engaged multiple times in a The fallback content to display on prerendering, you can use the armor on each engage (as long as you don't The fallback content to display on prerendering it which causes it to be The fallback content to display on prerendering).
SourceWhen do you choose to Overtax?
When you overtax armor, you can wait to see what the The fallback content to display on prerendering before deciding if you want to overtax it.
Source