Mini Stealth Cards are a rare item which when activated will make the player's Gear invisible to enemy monsters. This causes all monsters to be "passive" to the player - meaning they will not attack unless the player attacks them first, or another monster within their vicinity (it will not however make the player stealth to players of the opposing nation).
Currently Mini Stealth Cards can only be purchased with mileage points on SubaGames' website, and can occasionally be awarded to players by a GM in-game if they are logged in at the time. Transparent Cards are also unavailable to sell via the Selling Shop.
The War Point Shop has an item called a Transparent Card for sale which is described as an ingredient for making Mini Stealth Cards - however there is currently no Factory recipe available to create a Mini Stealth Card, making the item effectively useless.
It is rumoured that another material known as "Transparent Osmium" will be released in a future update which will be used along with the Transparent Card to create a Mini Stealth Card - however there is currently no word from the developer on if/when this will happen.