Can you provide some stats on the item and how it would work? (Saying it would work the same exact way as what the enemy does would be unoriginal.) Here's a suggestion:
Bubble Pack
Accessory
"Provides a defensive shield when equipped. If popped, it must recharge."
Gives the "Bubble Shield" buff when equipped. When the buff dissapears, it must wait a minute before the shield can reactivate.
Buff: Bubble Shield - This buff will put a defensive bubble around the player. Whenever you are hit, you take no damage and the bubble absorbs it. The bubble can only take 300 damage before it pops; your defense is not taken into account for this bubble, it will take full damage from all enemies. Once popped, the bubble will need a minute to recharge.
"A bubble that defends you from 300 damage."
In order to prevent people from unequipping and equipping the accessory over and over, the bubble "cooldown" will only count down when the accessory is equipped. So if you take the accessory off, the time before the bubble recharges only goes down the accessory is equipped. If you take off the accessory when the bubble is on you, the bubble dissapears and will keep the health it had from when you took it off. This accessory is universal for the character and equiping another pack will have the same status as another pack. (ex: your bubble pops, you take the pack off. you put on another pack, but the same cooldown will be applied. or you have a 100 health left on the bubble, you equip another, the other pack will still have a 100 health bubble.)
Something like this could be cool. Of course, this is my suggestion, so it may not be balanced to your or other's liking.