It's called cloak spell or invisibility spell. What it does is it has a ring that if placed over a group of units in the ring they become invisible for 5 seconds and while invisible the towers can't attack them because they don't see them. The time would be increased by two every upgrade and max upgrade is three at 9 seconds. The stats are 32000 elixir 45 min time and five second duration and Max troops it cloaks is 25 unit spaces for ex it could cloak 25 archers or one pekka but not both at the same time. That also increases as u upgrade it by 5 units every time. Let me know what you think