The way this spell would work is it reduces the troops size, hitpoints, speed movement, and strength by half. This spell should only work for small ground troops though like barbs, archers, and goblins. When the shrink spell is placed on one of these 3 troops it should miniturize them and they should be undetected by defece units for a short period of time until the spell wears out. The starting cost for this spell should be 20,000 elixir and should be available at townhall 9 and 10.