Mosquito Hell is the fourth stage in Summer Diary.
The battle opens with some Hippoes, a Metal Hippoe and a Teacher Bear. Once the base is hit, Carny Otta, Pigge, St. Pigge the 2nd, Firework Guys will spawn with a boss wave. A maximum of 4-5 Carny Ottas will be sent out during the battle.
Simple meatshielding with your long ranged attackers is enough. You may use Anti-Red cats (Axe Cat, Fish Cat) to deal with St. Pigge the 2nd if you like.