World Destruction Gun

The weapon of mass destruction that is your final masterpiece is finally done! Quick! You must destroy the heroes before they get to it! After killing enough heroes, you must collect the final ingredients to finish the secret syrup to activate your cannon! ^ How does that sound as an idea for the object of the game? So, the idea is basically that while collecting resources to build towers, you try to save up the right resources to make the syrup and then activate the cannon; you can get all the resources except one just like the ones you can for tower building and the final ingredient can only be obtained by killing a huge boss superhero that comes at the end of a fairly high up level.

Here is a prototype for the cannon: