The Boss ability may be played at any time during Adventure Phase, even if your adventure phase is already over (as long as you have a target-able Hero that survived your dungeon this turn). Once Adventure Phase is over, you can no longer play this Item.
A Hero with this Item takes no damage from the first three Rooms in your dungeon, including abilities that increase a Room’s damage. It is still affected by abilities and can be killed by effects like Bottomless Pit's “destroy this Room” ability.
The first three Rooms are counted from left to right, and deactivated Rooms do not count against that total.
Removed Heroes are ignored for the rest of the game. They cannot be the target of any Spells, Abilities, or Items and do not return to the Town.
This card may be a reference to the famous invincibility star from the Super Mario series.