The problem with the lava tank is that the slow projectiles are seen as a disadvantage. Actually, it's a lot harder to avoid them, as soon as you see a lava ball you don't have to dodge it right away, you just wait 2 seconds until they arrive and you're distracted. Due to the slow projectiles it is possible to have many lava balls on the map at the same time. In my opinion the strongest tank at the moment.
